Israeli geologists caused a minor stir in the 1960s when they announced the discovery of a concrete compound in a twelve-million-year-old rock formation in the Negev desert.1 This news raised eyebrows, particularly among engineering historians, archaeologists, and paleontologists, for the discovery predated not only the earliest known use of concrete but also the earliest known hominids. Twelve million years ago, our ancestors were hardly more advanced than today's lemurs. Who made the concrete?
Predictably, the facts are less sensational than the headlines. The pseudo-concrete was created when geologic forces gradually brought a limestone outcrop into contact with oil shale and, with water as a catalyst, produced a natural cement compound. This compound would not be considered concrete by chemists or engineers; rather, it could more accurately be described as “bad asphalt.” For this reason, I think it best to confine our examination of concrete's origins to those early human societies whose approach to its invention, while sometimes not quite scientific, was more methodical and successful than Nature's random products.
Because lime—sometimes called “quicklime”—is the essential ingredient of concrete, it is perhaps best to begin our story with the discovery of that remarkable substance. Lime is derived from the principal component of limestone: calcium carbonate. Limestone is created from the physical remains of countless generations of corals and shellfish that eventually formed a thick sedimentary layer. This layer was eventually crushed and crystallized by powerful geologic forces, resulting in a whitish rock. Pick up a sun-bleached seashell lying on the beach, and you are, in effect, holding a pure form of lime-stone, for the shell consists almost entirely of calcium carbonate. Limestone in its abundance provides silent testimony to the massive volume of life that thrived in the oceans for hundreds of millions of years before human beings came into existence. And those human beings would eventually discover that limestone contained hidden properties that, to their primitive eyes, seemed nothing short of miraculous. Even for us today, long inured to technical wonders, these properties still seem a little eerie and preternatural.
We now know that lime was discovered sometime toward the end of the Paleolithic Age, approximately twelve thousand years ago. The Paleolithic (Old Stone) Age reaches back almost three million years, and technically begins with the first stone tools. Consequently, it encompasses both the hominids and anatomically modern humans who used stone tools. For Homo sapiens, the Paleolithic Age begins with our species, approximately two hundred thousand years ago.
Until the invention of carbon-14 analysis and other sophisticated dating technologies, it was often difficult for archaeologists to differentiate the age of objects found at various sites where our Paleolithic ancestors once lived. Were the objects one hundred thousand years old? Sixty thousand years old? There was sometimes not enough variation among the artifacts to easily chart a firm evolutionary path in toolmaking. For us, technological breakthroughs happen constantly within a single lifetime; for our hunter-gatherer ancestors, they took place perhaps once every hundred generations or more. For most of our existence on this planet, we were pretty slow on the uptake when it came to technology.
Then something happened between fifty and sixty thousand years ago. Stone tools gradually improved, and the diversity of artifacts increased. Around this time, the earliest bow was invented, and the sophistication of spear and axes improved.2 The first artwork arose; people began painting on cave walls and carving primitive figures in bone. One result of these small but immeasurably important developments was that when our ancestors first entered Europe forty thousand years ago, they possessed a decisive technological edge over the Neanderthals they encountered there. If modern humans had immigrated to Europe twenty thousand years earlier, this might be a completely different book.
After this technological uptick, a period of stasis returned that lasted millennia. The Neolithic (New Stone) Age began around 10,000 BCE. Compared to the slow pace of change during the Paleolithic Age, the Neolithic Age witnessed an explosive transformation in human societies and technologies. Ceramic figurines appeared, followed by pottery. Sheep were domesticated, and cloth weaving appeared soon after. Intertribal communities arose with shared languages and belief systems, and the larger labor pool led to the first great building projects. During this time, agriculture was gaining importance, increasingly supplementing the diet of hunter-gatherers with sowed grains and legumes. The modest leisure time afforded by food surpluses allowed for the discovery and development of new crafts. Some villages grew to become towns, and some of these towns would become the first cities.
Complex human societies had begun to emerge, and with them, what we may broadly call “civilization” had also arrived.
Archaeologists believed for a long time that the dramatic changes that took place during the Neolithic Age were primarily due to the discovery of agriculture and animal domestication. Only recently have we come to realize that the story is much more complicated than that. Technological and societal revolutions began centuries before agriculture arose.3 The old demarcations between the Neolithic and Paleolithic Ages have recently been pushed back and become blurred.4 These societal changes may have begun with the discovery of that remarkable substance: lime.
The most popular theory of lime's discovery is the “campfire on limestone” scenario.5 It runs something like this: At some point in the distant past, a group of hunter-gatherers pick a convenient spot for foraging and settle in for a few weeks or months. As a safety precaution, they locate their fire pit in a small depression on a stony outcrop well isolated from any dry brush. On this occasion, they build their fire in a limestone declivity. After some days or weeks have passed, they notice that the stone near the flames becomes desiccated and breaks off into clumps that easily collapse into a white powder. This is lime. After the fire has been extinguished and the pit becomes cool, someone picks up one of the clumps and crushes it in his hand. He feels a slightly painful irritation caused by the caustic powder. After first shaking his hand violently to remove the powder, he then pours some water on the affected skin to remove the nuisance. This normal response to an irritant is, on this occasion, not a very wise move. The water provokes a powerful reaction with the powder, and what had merely caused irritation a moment earlier now produces a chemical burn. Frenzied with pain, he continues to pour water on his palm and fingers. Fortunately, the more water he pours, the greater the dilution of the reactive compound, and soon the pain is lessened. Red, blistery patches—the scarring caused by second-degree burns—remain on his hand.
Of course, the victim goes to a doctor. It does not matter that the physician in question is a witch doctor, for the tribe's medical practitioner is not only the font of countless spells accumulated from an oral tradition that dates back from time immemorial, but he is also the chief pharmacist, possessing a repertoire of cures or palliatives that comprise hundreds of plant and animal parts. Perhaps less than a quarter of the ingredients in his medical arsenal represent true cures or analgesics, and the rest are placebos. However, between the panaceas and a few real herbal remedies, the shaman probably enjoys a high success rate—most people survive their illnesses naturally—which reinforces his people's faith in him.
After he dresses his patient's wound and gives him the Paleolithic equivalent of two aspirins, the shaman decides to investigate the curious powder that caused the problem. He knows that people confronted with a painful experience are not the best witnesses, and so he probably doubts the story about water causing the powder to burn. After all, water is used to put out fires, right? Bathing in it on a hot day cools the body and drinking it slakes one's thirst. It soothes pain but does not cause it.
The shaman goes to the fire pit and uses a stick to scrape some of the powdery rock into a small basket or clay bowl. Perhaps he first sticks the tip of his left pinkie into the powder and discovers that, yep, it is a mild irritant. Then he adds a little water to the powder. What happens next no doubt amazes him: the mixture begins to generate a flameless heat. His patient was not deranged after all; this is some serious stuff. As he continues to watch the bubbling concoction, he observes that after a few minutes the foaming dies down and the heat diminishes. If the witch doctor is patient, he will notice that the substance soon becomes solid. He taps the material with a stick and confirms that it has become very hard. A rock has been created!
Today we know what the shaman did not: that the heat of the fire transformed the calcium carbonate of the limestone. All the carbon dioxide and water within the rock (yes, all rocks contain a small degree of water) will have evaporated, leaving behind calcium oxide: the caustic powder we call lime or quicklime. When water is added to the powder, a violent chemical reaction takes place: heat is generated—up to 150°C (over 300°F)—and calcium hydroxide is formed. This new compound craves the carbon dioxide it lost during the baking process and so pulls it from the atmosphere like some alien creature dying of asphyxiation. Calcium carbonate begins to form within the mixture, and after a short time, it hardens and becomes, in effect, limestone once again. This artificially created calcium carbonate is very white and very hard. One might view it as the purest form of concrete.
Until very recently, the importance of this discovery was not fully appreciated. Archaeologists reasoned that a humble substance created by a simple campfire could not have had that much effect on the course of human technological development. This perspective was almost universally held until the 1990s, when new excavations and a closer look at the empirical evidence would challenge that assumption.6 Indeed, it is possible that the revolutions that led to the Neolithic Age may have begun with the invention of concrete, and that lime's discovery was far stranger and more interesting than anyone had previously supposed.
A RADICAL NEW VIEW OF THE LATE STONE AGE
In 1963, members of a joint American-Turkish archaeological survey team from the University of Istanbul and the Oriental Institute of the University of Chicago combed the landscape of southeastern Turkey, looking for sites to catalog for possible future excavation. In the small province of 
anliurfa, not far from the Syrian border, they found an exceptional number of potential sites for exploration. Toward the end of their survey in the province, the archaeologists came to a large hill with a rounded top that the Turks called Göbekli Tepe, which means “potbellied mount.” The hill is a little over 300 m (ca. 1,000 ft) high and lies at the base of the Taurus Mountains. Nothing about the hill sets it apart from the others, except that its particular position provides superb views in all directions, the most spectacular being the mountains to the north and the Harran Plain to the south. However, the hill's immediate vicinity holds a particular and powerful interest for historians and biblical scholars. Turkey has a very rich past, and the southeastern region of the country, known since ancient times as Anatolia, has an even richer heritage. The tiny Anatolian province of Sanliurfa is especially drenched in prehistory, history, myth, and—incorporating varying mixtures of all three—tales central to Judeo-Christian and Islamic traditions.
Over the millennia, this diminutive region has been conquered and ruled by the Sumerians, Akkadians, Babylonians, Assyrians, Hittites, Hurris, Aramaeans, Medes, Persians, Macedonians, Romans, Parthians, Armenians, Arabs, Kurds, Crusaders, and, finally, the Turks. Near Göbekli Tepe is the ancient city of Harran, for which the plain is named. According to local Islamic tradition, Harran was the first spot where Adam and Eve stopped after their expulsion from the Garden of Eden.7 The Bible tells us that Harran is also the place where Terah and his son, Abram (the future patriarch Abraham), Abram's wife, Sarah, and their son, Lot (whose future wife would morph into sodium chloride) settled in for a spell on their oftdelayed journey from Ur to Canaan.8
Also nearby is the province's eponymous capital, Sanliurfa, more commonly known as Urfa. According to Turkish Islamic tradition, Urfa was originally the city of Ur, the birthplace of the aforementioned Abraham.9 (Most archaeologists place Ur in today's Iraq.) According to Jewish legend, it was in Ur that Abraham was thrown into a great bonfire by the nasty Babylonian king Nimrod.10 God intervened on Abraham's behalf, and he walked out of the flames unscathed. Turkish Islamic tradition explains why: God had turned the flames into water and the firebrands into fishes.11 To commemorate Abraham's deliverance from the flames, Urfa has for many centuries maintained a sacred pool of fishes next to the mosque dedicated to the patriarch.
Moving on to more verifiable history, the plain just outside Harran was the scene of some of the most significant battles in antiquity. It was on the Harran Plain where the Babylonians defeated the Assyrians in 610 BCE; where Xenophon and his Ten Thousand marched by in 401 BCE, harried by the Kurds along the way;12 where Marcus Licinius Crassus, the Roman general who had defeated the rebel slaves led by Spartacus, was himself defeated by the Parthians in 53 BCE;13 where the Roman emperor Caracalla was assassinated by one of his lieutenants during another campaign against the Parthians in 217;14 where another Roman emperor, Valerian, was decisively beaten by the Persians in 260 and taken captive;15 and where the crusaders fought the Turks in the Battle of Harran in 1104 (the Crusaders lost).16
In short, today's tiny Sanliurfa province has seen the rise and fall of many kings, sultans, shahs, emperors, emirs, and pashas, as well as their respective kingdoms, empires, and emirates. Hardly a day goes by without some farmer discovering an ancient artifact while digging a well or tilling a field.
By the time the archaeologists came to Göbekli Tepe, they had already recorded a number of exciting sites for excavation and were getting a little jaded by this surfeit of riches. Some requisite exploratory digging at Göbekli Tepe uncovered a large number of ancient flint and obsidian tools. However, a few carefully carved limestone blocks poking out of the ground seemed to belong to a much later period. The director of the survey, Peter Benedict, guessed that a Byzantine church and cemetery overlay a more ancient settlement. In a region abundant in important sites, Göbekli Tepe did not appear all that interesting. Benedict noted the geographical coordinates of the hill, wrote a brief description of the stone tools and carved stone blocks found there, and gave the site a name that, while hardly prosaic, was eminently practical for cataloging purposes: “V 52/1.”17 Bennett and the other members of the survey team then moved on to look for other potential sites. None of them would have guessed that the hill would one day be the site of one of most important archaeological discoveries of all time and provide the final piece of an archaeological puzzle that had taken over a half century to put together. For, in addition to its religious and historical claims to fame, Lilliputian Sanliurfa province would be revealed as the birthplace of civilization.18
One site that had appeared very interesting to the surveyors was located 96 km (ca. 60 miles) to the northeast of Göbekli Tepe, at a spot called Çayönü, near the historic town of Diyarbakir. Less than a year later, in 1964, Chicago University's leading Middle East specialist, Robert Braidwood, accompanied by his wife and colleague, Linda, arrived at Çayönü to begin excavating the site.
The Braidwoods were members of that generation of archaeologists who followed the exuberant pioneers of the nineteenth and early twentieth centuries; people like Heinrich Schliemann, discoverer of Troy; and Robert Evans, who uncovered the Minoan capital at Knossos in Crete. Schliemann and Evans were both accused of rushing excavations in feverish attempts to unearth the most spectacular artifact or treasure, while tossing aside seemingly insignificant items that could reveal much about the cultures they were supposedly bringing to light.19 A gold death mask may be impressive, but it tells us less about the man behind it than do the bones or shells of the animals he ate for supper, or the seeds or pits from the fruits he enjoyed for dessert, or the last surviving threads of the clothes he wore. Evans and Schliemann also brought with them rather romantic notions based on the Greek myths, and this seriously colored their interpretation of the data. To be fair, both men had no manual or established procedures on how to dig up the remains of an ancient civilization, and their spectacular finds did herald the beginnings of a new scientific field that would eventually be called “archaeology.” Nevertheless, their work left much to be desired.
The Braidwoods and their colleagues were of a different breed. They designed the rigorous methods now universally used to perform an excavation: the laying out of a string gridline over the site, the shaking of each spade of dirt through a fine screen to capture the smallest artifact fragment or trace of food detritus, and the meticulous recording and cataloging of everything found. Braidwood was also among the first archaeologists to recognize the importance of using radiocarbon analysis to more accurately date artifacts.20 Developed in 1949 by Willard Libby and others at the University of Chicago (Braidwood's home base), the technology measures the decay rate of the naturally occurring radioisotope, carbon-14, which is found in the remains of all organic material less than sixty thousand years old (little of the isotope remains after that period of time has passed). Like many other important innovations, radiocarbon dating was not immediately or enthusiastically embraced by all those who would most benefit from the technology. Braidwood's contemporary, British archaeologist Stuart Piggott, denounced radiocarbon analysis as “unacceptable,” largely because it contradicted the dates and chronologies he had put forward in his work on Neolithic sites.21 Widespread acceptance of radiocarbon dating did not come about until the 1960s, by which time Braidwood had already been using it with great success for almost twenty years. The innovations advanced by Braidwood and others in the post-World War II period would forever change the science of archaeology.
By the time he came to Çayönü, Braidwood had been surveying, excavating, and studying the artifacts of Middle Eastern archaeological sites for over thirty years, mostly in Iran and Iraq. Like most archaeologists, he believed that the earliest civilization arose somewhere in the Fertile Crescent, that imaginary arch that begins in the Nile delta and runs through the Levant (where today's Israel and Lebanon are located) and then turns east to end in the lower reaches of the Tigris and Euphrates Rivers. During their work in northern Iraq and Iran, the Braidwoods were beginning to come to a slightly different conclusion about the rise of civilization in the Near East than that proposed by other prominent authorities like James Breasted and V. Gordon Childe. While Breasted and Childe believed that the first settlements had sprung up in the lower reaches of the Tigris and Euphrates Rivers, where rich alluvial soil afforded abundant opportunities for agriculture, the evidence the Braidwoods were uncovering instead pointed to the foothills of the Taurus and Zagros Mountains, stretching from southern Turkey to northern Iran.22 They discovered that the older the agricultural sites were, the farther north they were found. Robert Braidwood called this area the “hilly flanks” of the Fertile Crescent. This made perfect sense. During the earliest stages of agriculture, people were still learning how the planting process worked. And since the first cultivated cereal crops yielded barely more than their wild cousins, these proto-farmers probably needed to hunt game to supplement their diet. The hills were abundant with game, and their forested slopes allowed hunters greater opportunities to sneak up to their prey than did the open plains to the south. Moreover, since farming requires settling down and living at a fixed location, the domestication of some of these game animals also made sense. The archaeological record pointed to sheep and goats—natural denizens of craggy mountains and hills—as the first domesticated farm animals. The critical transition had to have taken place in a hilly or mountainous region. When the Braidwoods came to Çayönü in 1964, they knew that exploratory digs conducted by the previous year's survey had turned up enough interesting material to suggest that this particular Neolithic settlement might be a key transitional site.
The first season's dig offered promise. It was clear that Çayönü was both quite ancient and, for an early Neolithic site, substantial in size. With each passing year, as the accumulated dust of the ages was brushed away and each fresh artifact brought to light, it became evident that Çayönü was indeed one of those critical missing links for which the Braidwoods had spent decades searching. Along with another settlement, Çatalhöyük, which the British archaeologist James Mellaart was excavating at the same time several hundred kilometers to the west23 (also on the “hilly flanks” of the Fertile Crescent), a solid picture was emerging of the hunter-to-farmer transitional period and of the growth of the first large settlements. Çayönü flourished around 7000 BCE and was the size of a small village. It is the earliest known permanent human community. It is in Çayönü that we see some of the earliest examples of farming, animal husbandry (pigs), woven cloth, copper metallurgy, and fired-clay ceramics.24 Nevertheless, all these crafts are at their earliest developmental stages. Aside from pork, the meat Çayönü's inhabitants consumed still came from wild game. There is no evidence that people at Çayönü milled grain, much less baked it, and all plants they ate were also gathered from the wild. Stone and bone were still used for virtually all tools. The copper and cloth artifacts discovered are primitive and, not surprisingly, seem like tentative first steps. The dwellings were constructed of sun-dried clay brick (adobe), and the structures were huddled close together, generally sharing a common wall. The ceilings were supported by a row of wood poles—the trunks of smaller trees. The entrance to the dwelling was through a hole in the roof that also served to evacuate smoke from the hearth. People climbed up ladders to reach the roof, then pulled them up to use for the ceiling entrance, a defensive arrangement found to this day in some villages in the Middle East and North Africa.
Çatalhöyük flourished approximately seven hundred years after Çayönü and was about ten times the size of the earlier settlement. It is the oldest known “town” we know of.25 Besides its far larger size, several important technologies distinguished Çatalhöyük from its predecessor. Grain was stone-ground to produce flour and ovens were used to bake the first known bread, apparently unleavened. The ceramics crafts had also advanced in the seven-hundred-year interval. Instead of the simple firedclay figurines found at Çayönü, shards of the earliest known kilned pottery were unearthed at Çatalhöyük.26
At both Çayönü and Çatalhöyük, the floors of the dwellings were extraordinarily hard. Small pieces of limestone were set into what was initially assumed to be a hard adobe to form pleasant patterns. However, chemical tests established that the foundation material consisted of a mixture of lime with clay—the earliest known examples of artificial stone floors then uncovered. Archaeologists would call these “terrazzo floors,” because they resembled the flooring inlaid with marble chips that had originated in Terrazzo, Italy. This lime-clay mixture was also applied as a plaster for the adobe blocks used in constructing the dwellings at both sites. While the Braidwoods and Mellaart were impressed by this early use of lime for building, its true importance was obscured by the other Neolithic accomplishments, such as the evidence pointing to some of the earliest forms of agriculture, ceramics, and metallurgy.
Evidence confirming Robert Braidwood's theory about geographic origins of civilization was growing, and by the late 1970s the pieces were falling neatly into place. Braidwood was now convinced that the foothills of the Taurus Mountains in lower Anatolia, not the Zagros range to the east, was where civilization began to emerge, specifically in or near Sanliurfa province. He called this region the “nuclear zone,” meaning that the area formed the nucleus of where the first civilized crafts arose and where the transition from hunting to agriculture first took place: the “ground zero,” so to speak, of civilization.27 He was convinced that earlier, less developed settlements would be found not far from Çayönü and would thus complete the picture. Sadly, external events would interrupt the archaeologists' work. Sanliurfa province was about to become the ground zero of a very unpleasant war.
Southeastern Turkey had long been home to the Kurds, a people whose customs and language are closely related to those of the Iranians. When Mustafa Kemal Atatürk came to power in 1919, he brought the long moribund Ottoman Empire to an end and proclaimed his nation a republic and a “Turkey for the Turks.” In short, there was no place for the Kurdish language or culture in the new, westernized, secular Turkey.28 The Kurds had to become Turks—or else. It was not much different from the attempt by Americans of European ancestry in the late nineteenth and early twentieth centuries to make Native Americans “Americans.” (In both instances, the objects of conversion had been established on the land thousands of years before the arrival of the now dominant power.) The Turkish government labeled the Kurds “Mountain Turks” and outlawed their language.29 The Kurds defied the new government and sporadically revolted. Things gradually quieted down after a few years, with the Kurds passively resisting the conversion measures and the Turks generally ignoring the situation as long as their subjects behaved and paid their taxes. In 1984, after nearly six decades of simmering discontent, a Kurdish revolt broke out in Anatolia. It was led by a shadowy figure, Abdullah (“Apo”) Öcalan, who called for an independent Kurdistan. Southeastern Turkey exploded in violence. Turkish police were gunned down, and when troops were sent to Anatolia to restore order, they were ambushed as well. The government responded ruthlessly. People believed to be rebel sympathizers were either arrested or assassinated.30
Unfortunately for archaeologists, the Kurdish region of Turkey was also where most of the newly discovered or soon-to-be-discovered Neolithic sites were located. Especially affected by the violence was the region around Çayönü (Apo had grown up in a nearby village). The Braidwoods had no choice but to abandon the site and hired a local man to guard it. In an arrangement between the University of Istanbul and the University of Chicago, the former agreed to pay the guard's salary, while the latter offered to cover the cost of the man's food and bullets.31
The government's generous-carrot-and-ruthless-stick approach toward the Kurds in Anatolia resulted in a gradual winding down of the conflict in the 1990s, and in 1999 Öcalan was captured in Kenya, where he was remotely directing operations.32 Sadly, it was too late for the Braidwoods to return to Turkey: both were approaching their nineties, and their health had become too fragile for fieldwork.
Still, the Braidwoods had the pleasure of learning about recent discoveries that confirmed their theories about where civilization had arisen. DNA analysis verified that all the species of wheat grown today throughout the world could trace their lineage back to a wild variety still growing in the foothills of the Taurus Mountains, near Sanliurfa.33 Further bolstering their theory was the discovery in the same area of two more Neolithic sites, both far older than Çatalhöyük and Çayönü. Taken together, the four sites would offer archaeologists a near-perfect chronology of how humans made the transition from hunter-gatherer groups to agricultural communities. Strangely, the buildings at both these newly discovered sites also had lime concrete floors.
The principal carrot offered by the Turkish government to the Kurdish population of Anatolia was a vast infrastructure upgrade for the region. Among these projects, which included road improvements and better schools, was the construction of a complex of large dams on the upper Tigris and Euphrates Rivers. These dams would prevent seasonal flooding, provide the local inhabitants cheap hydroelectric power, and offer a steady and controlled source of water for agriculture. It was like America's Depression-era TVA Project on steroids.34 The downside to all this was that dozens of important archaeological sites—many still unexcavated—would be flooded.35 One site destined to be lost to the floodwaters was Nevali Çori, a Neolithic settlement that showed promise after an earlier exploratory dig had produced interesting artifacts. The University of Istanbul and the University of Heidelberg quickly organized a rescue project in 1993, and excavation began soon after under the direction of German archaeologist Harald Hauptmann. As with Çayönü, Nevali Çori proved to be another key “missing link” in the story of the rise of civilization.
Dr. Hauptmann and his colleagues established that Nevali Çori flourished five centuries earlier than Çayönü, and although it shared certain common features with the latter site, such as fired-clay figurines and terrazzo lime concrete floors, it was distinctly different. Not surprisingly, some technologies were more primitive, while others were yet to be discovered. Woven cloth and copper metallurgy had yet to make an appearance at that time. In one technology, however, the people at Nevali Çori showed more mastery than their later, near-contemporary Neolithic brethren.36 Dr. Hauptmann was amazed to discover large, intricately carved limestone blocks and tall monumental pillars shaped in the form of a “T.” To cut limestone using flint is a tedious business, yet these blocks and pillars were carved with great care and surprising mastery. The pillars were approximately 3 m (ca. 10 ft) tall and once supported a wooden roof. Incised on them were sculptures, including the earliest known relief of human hands.37 Remarkably, the hands seem to be clasped in prayer. The stonework would not have been out of place in a site dating several thousand years after Nevali Çori. A limestone bust of a man's head—the earliest known life-size anthropomorphic figure—was also discovered. The man's head is bald, except for what appears to be a crawling snake on top—or his hair cut to resemble a crawling snake—and may represent a shaman or priest.38
Another thing that set Nevali Çori apart was that it seemed to be more a religious complex than a settlement. Of the twenty-two buildings unearthed, only a few seem to have been continuously occupied dwellings, perhaps the living quarters of priests, priestesses, or shamans.
The rescue operation to excavate and survey Nevali Çori was largely a success, and many tools, utensils, and limestone carvings were recovered before the river waters confined by the new Kemal Atatürk Dam flooded the site.
As one Neolithic site was being submerged, another site was emerging a few kilometers away, at a place that had been cataloged thirty-five years earlier and was filed under the name “V 52/1.” Its discovery would rewrite all the books about the late Stone Age.
GÖBEKLI TEPE
Among those who worked under Harald Hauptmann at Nevali Çori was Dr. Klaus Schmidt, another professor of archaeology at the University of Heidelberg. The carved limestone blocks at Nevali Çori reminded him of those that had been exposed at a site mentioned in the 1963 survey by Peter Benedict. If the stones at Göbekli Tepe were indeed Neolithic carvings—and not the remains of a medieval church—this would explain the flint tools discovered by Benedict, who had assumed they belonged to a far earlier period and stratum.39
Plans were made to excavate Göbekli Tepe, and serious work on the site began the following year in a joint project conducted by Turkey's Sanliurfa Museum and the German Archaeological Institute.
After the archaeologists had set up their grid lines and carefully started their excavation work, they were befuddled with what they began uncovering at Göbekli Tepe. The stonework was similar to that of Nevali Çori but was in some ways even better. Dressed stone masonry was used for walls, and, like Nevali Çori, limestone was carved into “T” crosses that served as pillars for a now-vanished wooden roof. Dr. Schmidt believes that large teams of people were organized to pull massive limestone blocks—some weighing up to fifty tons—from a quarry two kilometers away. For the largest blocks, Schmidt estimates that work crews numbering up to five hundred people were assembled for the task—an astonishing and unprecedented number of individuals cooperating together during this early period.40 Once the limestone blocks were put into place, the builders then carved them with a dexterity that would not be seen again for many centuries. Bulls, cranes, foxes, boars—the totem figures of a foraging people—were rendered with a deft likeness. And nowhere is there any evidence of agriculture, only the food detritus of hunter-gatherers: wild animal bones and remains of seeds and nuts.41
It is conjectured that some sort of common belief system and shared customs and language brought a thousand or more hunter-gatherers each year to this spot, which apparently held some spiritual significance for them. And together they planned and built a massive religious center that has no equal for its time, for the results of the carbon dating tests staggered the archaeologists: the temple complex had been created 11,600 years ago,42 almost 7,000 years before the creation of the Stonehenge monoliths and predating Nevali Çori by a thousand years. At the time building began at Göbekli Tepe, humans in North America were still hunting wooly mammoths and avoiding sabertooth tigers. The last Neanderthals had only recently gone extinct, and the last members of a far more primitive hominid, Homo floresiensis, might have still been dodging modern humans in Indonesia.43 As far as we know, there was no place on the face of the earth that could even approach the construction mastery of Göbekli Tepe, let alone equal it.
Göbekli Tepe was without doubt a sacred precinct, for there is no sign of permanent human habitation at the site. Apparently, these ancient people reserved their finest structures for the divine and would continue to do so for many centuries, as evidenced by Nevali Çori. As Dr. Schmidt puts it: “First the temple, then the town.” (Zuerst kam der Tempel, dann die Stadt.)44 And, as at Çayönü, Çatalhöyük, and Nevali Çori, these people burned limestone to make concrete flooring.
In early 2003, not long after the Braidwoods learned of the exciting data coming from the excavation at Göbekli Tepe, both came down with severe bronchial pneumonia and were taken to University of Chicago Hospital. A few days later, in a poetic denouement that the gods sometimes grant to inseparable lifelong partners, the Braidwoods died within hours of each other. Robert was ninety-five, Linda, ninety-three.45
CONCRETE: MOTHER OF INVENTION
Toward the end of the twentieth century, archaeologists who specialized in materials engineering, now called archaeomineralogists, began pondering ancient concrete's importance. They noticed that as one goes further back in time, the technologies begin disappearing one by one: oven-baked food vanishes, then pottery, then woven cloth, then metallurgy, then simple ceramics, and finally, primitive agriculture. At almost twelve thousand years in the past, all the remaining technologies—at least those not related to hunting-gathering—are pretty much the products of limestone: carved reliefs, block masonry, lime plaster, and lime concrete floors. Indeed, this mineral dominated the last years of the Paleolithic Age, which alerted archaeomineralogists to the possible importance of lime in the technological revolution seen in the succeeding Neolithic period.46 They also began to realize that the discovery of lime was far more difficult and complex than previously believed.
That archaeologists had not realized the importance of lime was largely due to a simple misunderstanding: almost everyone was under the impression that the substance is easily made; that all you had to do was make a fire in a limestone declivity to create lime. Some had even suggested that the discovery of lime was as old as the history of fire. After all, humans had been manipulating the properties of rocks with heat for many thousands of years. By simply putting flint in a fire for a couple of hours, the stone becomes easier to chip—or “knap”—for the purpose of making spear blades, arrowheads, and axes.47 Many authorities have long assumed that the discovery of lime had similar origins, and one form or another of the scenario noted earlier in this chapter is the most widely believed version.48
Unfortunately, few people apparently took the trouble to actually test this theory with some limestone.49 If they had, they would have discovered that it is extremely difficult for a campfire to reach temperatures high enough (848°C / 1558°F) to extract lime from the surrounding rock. To put this into perspective, this level of heat is three times higher than what a modern kitchen oven can produce. Even at this temperature, extracting lime is a difficult proposition, since that part of the limestone beyond the point of direct exposure to the heat acts as an insulator. Because of this insulating effect, some limekilns have actually been built of limestone. (Modern rotary kilns heated by blast furnaces do not have this problem, as all sides of the stone are thoroughly baked.) For this reason, our ancestors had to create high-temperature kilns to make lime.
Our ancient ancestors made two key discoveries that eventually led to modern civilization. The first—and most important—of these two discoveries was agriculture. However, agriculture came after the earliest kiln-based crafts, what we now call “pyrotechnologies.” The cultivation of crops came many centuries after the first major building projects, as well as the extended social bonds that sustained the cooperative efforts behind such achievements. It was not farming that brought large groups of people together but some spiritual yearning, a religious impulse strong enough to prompt the building of a huge temple complex. Göbekli Tepe may have been the focal point of the first “organized” religion—in other words, a Stone Age Jerusalem. It is my suggestion that, in addition to the spiritual yearning and extended societal bonds that led to the creation of the temple complex, another factor was involved. It was a physical phenomenon that seemed magical to these Paleolithic peoples: the chemistry of lime.
Besides underestimating the difficulty in generating the amount of heat required to produce lime, archaeologists also undervalued the impact that the properties of this amazing substance must have had on pre-Neolithic humans. It is difficult to erase from our minds the technologies we enjoy today and supplant them with the very limited knowledge and tools possessed by our Paleolithic ancestors. The curious properties of lime must have upended everything rational to them. It produced heat when it came into contact with water and created—to all appearances—a true rock, not something flimsy like dried clay. Mix it with a little sand or clay, and you could make a larger rock. In a way, it must have seemed like some divine power transferred to humankind, for only the gods could make rocks. The “magic” of lime may have given its discoverer a power that soon transcended the immediate hunter-gatherer group and led to the first intertribal communities based on a particular belief system and set of rituals.
The discovery of lime also seems to have coincided with some of the earliest instances of carving limestone for construction purposes or to create art. It is as if the discovery of lime focused people's attention for the first time on the other attributes of limestone, especially the fact that it is the most malleable of all the hard rocks. As lime was almost certainly considered a sacred substance, so must have limestone been regarded as a sacred rock, for its use—both in construction and art—was, like lime concrete, restricted for many centuries to religious complexes like Göbekli Tepe and Nevali Çori.
It is also likely that the process of making lime remained a closely guarded secret of the priests or shamans, for no limekiln has been discovered within the precincts of these late Paleolithic and early Neolithic sites. (The limestone was probably kilned at a remote location, away from the prying eyes of the profane.) And this high-temperature kilning process was easily the most technologically difficult, most physically demanding, and likely the most resource-intensive craft during this period of prehistory.
Since the art of kilning limestone changed little from remote antiquity until the early industrial age, it would be worthwhile to look at the process as it was practiced for such a long period. The first step was to create an oven in which an enclosed fire could concentrate the heat. This was done by digging a shallow pit and then building a stone structure—eventually brick would be used—around it that could contain and intensify the heat and allow just enough air to enter to keep the fuel burning at a high temperature. Over the centuries, this would assume the shape of a beehive or a Burgundy wine bottle. The “neck” of the bottle-shaped structure functioned as a constricted chimney that helped to keep the interior of the kiln extremely hot during the firing process. A small aperture at the kiln's base, just large enough for someone to crawl inside when it was fully open, controlled the amount of air reaching the flames and enabled the adding of more fuel. Once the structure had been completed, men would crawl through the opening to tightly stacked firewood in the pit and then place pieces of limestone—usually the size of a small fist or smaller—over the wood. More wood was then stacked on top of the layer of limestone. The reason the limestone was no more than fist-size was to allow the heat to completely permeate the stone and fully calcify it. The wood stacking and limestone placement alone usually required a day to complete. The kiln workers would then carefully crawl out of the oven, set the wood alight, and then close the opening with a flat rock, leaving it ajar enough to permit a steady flow of air to feed the fire. Once the fire was started, it needed to be worked regularly; men would poke the embers, fan the flames, and continually add more wood every hour or so.
The firing often lasted three days and two nights. Because the firing had to be carefully managed during this period, the work was almost always performed by at least two people. So much heat would be generated in the kilning process that another two days were required after the firing to allow the oven's interior to cool down enough to permit the workers to go inside to remove the calcinated lime. Removing the lime was a hazardous undertaking. As we have seen, lime is very caustic, and handling it can cause skin bums, so gloves or some other protective intermediary were used. (Neolithic people probably utilized animal skins.) The most dangerous aspect of the work was the risk of getting lime dust in the eyes, throat, or lungs. Since water is the activating agent, the effect of calcium oxide settling on moist parts of the human anatomy would be deleterious, to say the least. It is probable that many early limekiln workers suffered from diminished vision, a variety of pulmonary ailments, and, eventually, abbreviated life spans as well. Kilning lime was grueling work and was usually performed by slaves during the Greco-Roman period and in the antebellum American South.50
In the early Neolithic, the limekiln most likely was not an aboveground structure but simply a deep pit. Controlling the airflow and adding fuel was probably managed by placing flat rocks over the pit, with two men on each side moving them around with heavy sticks (the rocks would have been too hot to touch with hands).
Since even a modest limekiln required large amounts of fuel, collecting the necessary wood would have involved much effort, especially in late Paleolithic and early Neolithic times because of the then-primitive nature of tools. Repeated blows by flint or obsidian axes against wood frequently fractured their blades; yet, the blades would be replaced and retied, and the work would be continued. At least a dozen cords of wood (a cord is a 4' × 4' × 8' stack of wood) were probably used in a single firing of a small kiln. As human populations grew, large swaths of forests would be leveled to provide the wood for limekilns.
Kilning limestone represented humankind's first use of complex chemistry. It was also the earliest known industrial process. Contemplating these ancient kiln workers—laboring away, covered with soot, being hit with a stifling blast of heat each time they fed fuel to the flames or adjusted the airflow—one cannot help but recall similar images from old photographs of the grimy laborers who slaved away in the soul-deadening factories of the Victorian Age, a dozen millennia in the future.
As odd as it may seem, the archaeological evidence shows that the earliest ovens created by humans were not low-temperature affairs for baking or roasting food but rather high-temperature limekilns. And this odd frog leap over simpler kilning methods paved the way for the key technologies that followed, as shown on page 49 (see table below).
It is no coincidence that fired ceramics make an appearance soon after the invention of the limekiln. Sun-dried clay bowls, while good for certain uses, often imparted a bad taste to the food or water stored in them. After the wonders of fired pottery were discovered, the only unkilned clay products that would remain in common use would be adobe bricks for building. By Sumerian times (ca. 4000-2500 BCE), it was a religious taboo to drink out of a sun-dried clay cup.51
Ceramic technology was quickly followed by metallurgy. Copper is typically found as an ore, unrecognizable from its final, processed form. However, on rare occasions, it does pop up in a somewhat pure state called “native copper.” One can shape native copper by repeated blows with a very hard rock to form a flat sheet. Still, it is a cumbersome endeavor that often leaves rocky impurities in the metal. On the other hand, by exposing the copper to high temperatures—even a couple hundred degrees short of its actual melting point—it becomes far more malleable. Since copper metallurgy arose after the invention of lime and ceramic kilns, it seems probable that the copper was put into a kiln to make it easier to work with. The temptation for a “let's see what happens when we stick this stuff in there” experiment would have been irresistible. By taking a branch and then splitting it at one end, the Neolithic smith had a convenient set of tongs with which to hold the native copper. Covering the branch with wet clay mud would have been sufficient to insulate it from the fire for the brief time needed to make the copper malleable enough for pounding.
As the efficiency of limekilns improved, it is possible that they could reach temperatures high enough to completely smelt the copper. Unlike limestone, where the insulating properties of the stone delay calcination, copper quickly liquefies once it reaches its melting point. After the advent of ceramics, a fired-clay bowl could now serve as a fireproof crucible in which the copper could be fully smelted. Fireproof clay molds would also allow the smith to cast a specific tool, like a sword or axe. However, these last innovations would come centuries later, and they probably coincided with another invention: the use of charcoal and the blacksmith's bellows.
However, the discovery of lime presents us with a very engaging mystery. Why would our Neolithic ancestors go to such tremendous effort to build and service a high-temperature kiln for the purpose of creating lime unless they first knew what the end product would be—and how would they know that?
Clearly, some extreme natural agency must have provided the inspiration, a geologic or atmospheric phenomenon demonstrating that limestone heated to a very high temperature will produce a “magical powder.” Only three natural forces on the face of the earth can reach temperatures high enough to calcify limestone: volcanism, lightning, and, on rare occasions, a forest fire. Let's look at them. Volcanism comes in two basic forms: explosive and effusive. An example of the explosive type would be the eruption of Mount St. Helens in 1980. A vast subterranean volcanic chamber of hot gases and molten rock builds up so much pressure that it eventually explodes with the force of a nuclear bomb. An example of the effusive type is the ongoing, languid flow of lava from Kilauea on the island of Hawaii. Volcanism is unlikely to have served Paleolithic peoples as a demonstrative agent for calcination. No one can closely observe the effect of an explosive eruption without being blown to smithereens or instantly carbonized by a pyroclastic avalanche. Slow lava flows, while far less dangerous (they typically advance at the speed of a crawling infant), almost always travel on older igneous (volcanic) rock, not limestone. Lava reaches temperatures high enough (700-1,300°C / 1,300-2,400°F) for calcination, but even if a fresh effusive flow were to crawl across limestone, the heat of the molten lava would obscure whatever effect it was producing on the rock directly beneath it.
Another candidate for calcinating limestone is a forest fire, which reportedly can produce temperatures approaching 1,200°C (2,192°F), but this is very rare even today and was much less common in ancient times. For example, active suppression of wildfires in North America for the last century has caused an unnatural buildup of vegetation that has resulted in very hot “high-intensity” fires. Only recently have we awakened to the fact that fires are a natural and essential part of all but the dampest environments. They enrich the soil and control noxious plant species, and the burnt vegetation serves as a chemical “wake-up call” to seeds buried beneath the surface. Natural fires tend to be “low-intensity” affairs that quickly sweep through an area, burning mostly grasses and brush and only lightly charring tree bark. The burn effects of low-intensity natural fires usually disappear within a few years.
However, high-intensity fires, while less frequent than now, certainly took place in ancient times. Vegetation could escape a natural low-intensity fire for a number of years and gradually accumulate. If a severe drought then occurred, followed by a natural (lightning) or human-made (campfire) ignition event, things could have gotten rather hot. Still, the fire itself, which burns at 380°-590°C / 720°-1,100°F, is not hot enough to create lime from limestone (it is not contained). Rather, it is the air above the fire that is capable of reaching the necessary temperatures, but only briefly. Another problem persists with this scenario. The dense growths necessary for the formation of a high-intensity fire are generally found where there is more soil than rock. However, it is just conceivable that ancient high-intensity fires took place below a limestone outcrop and burned hot enough and long enough to calcinate the limestone.
Was a forest fire the source of inspiration? It is possible, but unlikely. Hunter-gatherers would avoid burned-out areas because there was no longer anything to hunt or gather. The discovery of a freshly precooked carcass of, say, a deer might be the exception, but that would argue for a low-intensity fire, since a high-intensity blaze would have carbonized the carcass. Also, the evidence of calcination would have been eliminated with the first rainfall after the fire, since water transforms lime back to limestone; calcium oxide becoming calcium carbonate once again. Finally, limestone, like most rocks, acts as an insulator as well, one reason why it must be broken up into chunks no larger than a small fist. A forest fire burning on top of, or next to, a limestone outcrop will have little effect on it.
This leaves us with lightning, which, at first glance, seems as improbable as the other choices but is actually the best candidate. Satellite data show that lightning occurs roughly one hundred times per second around the globe.52 In some places, the number of lightning strikes per square kilometer (roughly 0.4 sq miles) of land is well over one hundred each year, and one hundred and fifty is not unheard of.53 And lightning can kill—and does so in a spectacular sound and light show. In 2010, one lightning bolt killed thirty-two people in two separate villages during a single storm in Pakistan.54 In 2005, another strike killed sixty-eight dairy cows in Australia.55 In the earliest literature, as well as in the later writings of the classical period,56 being struck by a lightning bolt was near the top of the list of deadly natural forces to be feared. For people who were outside much of the time, like our hunter-gatherer ancestors, the prospect of getting hit by lightning was particularly dreaded.
Yet, lightning was also considered a divine force. It was some sky god in action at the most direct and immediate level. Getting hit by lightning demonstrated that the victim had no doubt offended some deity—one reason why it was probably more feared than, say, a fatal illness. And since it was a divine force, the spot where lightning had struck the ground was considered holy by many early peoples.57 Adding to this imagined sanctity were the unusual artifacts discovered at the point of impact. For instance, if lightning strikes sand, a fulgurite is usually found. A fulgurite is created when a lightning bolt vitrifies the silica of the sand and forms a hollow glass tube. Fulgurites range from a few inches to over twelve feet long. They often resemble the shape of a lightning bolt, which accounts for another name given them: petrified lightning.
When lightning hits limestone, lime is created. The temperature of a lightning bolt is over 27,000°C (about 50,000°F), hotter than the face of the sun, so the “bake period” is instantaneous. While lightning is usually accompanied by rain—which would return the lime to limestone—sometimes it is not. At least one news story is filed each year about some golfer who, though seeing an oncoming storm, is little worried and decides to go for another hole and, as a result, is struck dead by a lightning bolt in broad daylight.
So, how did the people of the late Paleolithic discover that lightning produced lime? Let's revisit that ancient shaman we met earlier. This time he is gathering curative herbs in the mountains. Menacing clouds gather against the slopes, obscuring the sun, and the sky grows darker by the minute. The shaman knows that storms come fast and furious in the mountains, and so he decides that now would be a good time to return to his camp.
As luck would have it, as soon as he starts back home, rain begins to fall and the sky flashes with lightning that is quickly followed by a very loud thunderclap. Even primitive people understand that the period between a lightning's flash and its accompanying boom denotes how close the strike is, and so the shaman knows that this deadly force is very near. Suddenly he sees a lightning bolt strike the ground about fifty feet away. He squats down to make himself a smaller target for the obviously angry gods above and decides to ride out the storm. On this occasion, the storm quickly passes, and the shaman breathes a sigh of relief and perhaps offers up a prayer for his deliverance.
As we have seen, shamans are naturally curious about things; they probably possess the same strands of DNA held by scientists and good police detectives. The shaman walks over to look at the spot where the lightning struck the ground and finds that it landed on a limestone outcrop, scorching out a hole in the rock. The charred hole is surrounded by radiating cracks and a strange white powder (the sheltering trees prevented the brief rain from reaching this spot). The shaman picks up a pinch of the powder and makes the same painful discovery as our previous hypothetical primitive. The shaman experiments with it and, as in the earlier scenario, discovers that the powder is an amazing substance.
The shaman knows that lightning is hot and fiery. Accounts have no doubt been passed down of people being killed by it (and the resulting charred flesh and clothing), as well as its propensity for starting fires. The shaman understands that the powder was created by the especially intense heat and fire of the god-wielded lightning. He asks himself: “What if I could bring such heat to the rock? Would I also be able to produce this divine powder?” At this point, superstitious apprehension prompts a rationalization, and so he rephrases the question: “What if this god wanted me to witness the effects of the sky fire, so that I could also make this magical substance?” (It is easier to believe that you are following a god's will than usurping its power.) Inspired by this seemingly mystical experience, the shaman then spends perhaps ten or twenty years in trial-and-error experimentation in an attempt to get limestone to yield its strange white dust. Eventually, his efforts are rewarded. He wows his fellow tribesmen by showing them how he can make a hot, flameless heat using…water! And then, presto, a rock! Soon thereafter, he teaches his son and future shaman the secret of how to make the powder. The rest of the story is easy to guess: limestone comes to be regarded as a divine stone possessed with both hidden powers (its magical lime) and more commonplace qualities (its strength and ease of carving). Eventually, lime and limestone are used to create the first stone temple.
It is certainly within the realm of possibility that the shaman or his descendents chose the potbellied mount to build a temple complex because it may have been here that the revelatory lightning strike took place. Certainly, the hill would have been the highest point in the immediate vicinity and, so, especially vulnerable to lightning bolts. As with all ancient preliterate people, we will never know the full story and can only speculate about the nature of their gods or the inspiration for building such a grand religious center.
It would be centuries later, at the time of Çayönü and Çatalhöyük, that the lime would finally be used for secular dwellings as well. The once magical powder has now become nothing more than an everyday construction tool. Nevertheless, people would remain captivated by the counterintuitive properties of lime and its products.
Was the technological evolution in ancient Anatolia unique? Probably not. Excavations of the Dadiwan culture in China have revealed a large settlement that is roughly the same age and size of Çatalhöyük and that possesses the same crafts: agriculture, concrete, ceramics, and metallurgy.58 Neolithic sites in Serbia, such as Lepenski Vir,59 suggest a similar technological progression, including the use of concrete and carved limestone in a preagricultural, hunter-gatherer society.
However, what makes the excavations in Anatolia especially interesting is their extreme age and the fact that we have a fairly comprehensive picture of the progress of those social and technological revolutions. Excavations of more recent sites in the area also demonstrate that knowledge of these respective crafts were not lost to humanity through social upheavals or natural disasters. Agriculture continued on its course and was constantly refined and made more productive. Ceramics craftsmen would soon create products of great beauty and utility, while the blacksmith's forge would eventually produce both plows and lethal weapons. Lime and limestone construction would also remain in use. Eventually, they would be applied to constructing the most enduring and beautiful buildings of all time.
As for concrete, its story had just begun.