It’s not what’s on this island, but what’s beneath it, that interests me.
—JULES VERNE, JOURNEY TO THE CENTRE OF THE EARTH (1864)
In what’s known as the Valley of Mexico, concrete and asphalt flow from mountain slope to mountain slope, a sea made of pavement with countless buildings—houses, shacks, apartments, offices—riding the swells. Once, centuries ago, the valley was made of lakes, of fresh clear blues, including the most famous, Texcoco, where the Aztec empire was born. Those lake blues have vanished, their remains covered almost completely by a civilization made of asphalt and concrete. From an airplane window Mexico City is one vast spread of unending gray, accented with the ochre red of roofs and the dark pine of treetops, with only the rare patch of green ground to break the monotony.
Welcome to the quintessential megacity—defined as any urban area with ten million people or more. New York was the first, by 1950, and Tokyo followed soon after. Mexico City was the world’s third, passing the mark in the mid-1970s. Over the past century the world’s human population has grown exponentially (two billion in 1930, more than nine billion now), and the percentage of those people living in urban areas has grown along with it. As a result, the list of megacities had grown to twenty-eight by 2015; by 2030, Asia is projected to have at least thirty of its own.
To house, move, and support all these people will require a massive building boom, the likes of which the world has never seen. One gauge? Only twenty-five years ago, we were producing about three tons of concrete cement per year for every person on the planet; now that figure is closer to five. The explosive growth of Asian infrastructure leads the way—China alone makes and uses almost half the world’s supply—but the use of concrete is growing everywhere. Because concrete cement makes up only about 20 percent of the total weight of concrete (important fact: though many of us use the words interchangeably, “cement” and “concrete” are not the same), the amount of concrete being laid every year is probably twenty-five tons for every person in the world. All this making of concrete has enormous ecological consequences, including producing 10 to 15 percent of our CO2 emissions. It also says a lot about who we are as a species, and who we will be. “Concrete dominates the human environment,” Robert Courland, author of Concrete Planet, told me. “Nothing is as representative of modern society as steel-reinforced concrete.”
Mexico City is the perfect place to think about the consequences of all this paving and building. For one thing, under the combined weight of twenty-one million people and all their concrete, the city is rapidly sinking—over just the past half century an average total from locations around the city of more than thirty feet.
But the city is sinking not only because of what’s on the surface, but also what’s underneath. And what’s underneath the pavement are the two stories that have brought me to the Mexican capital. The first is a story of water, the second one of blood.
“Particularly in Mexico City we forget that we live within a lake,” says Luis Zambrano, an ecologist at the Universidad Nacional Autónoma de México. “Everyone thinks that the lake doesn’t exist anymore, and it exists.” The lake Zambrano’s talking about is Lake Texcoco, the site of the Aztecs’ capital city of Tenochtitlán, the city the Spanish destroyed in 1519 before building their own city on top of it.
Founded by the Aztecs (or the Méxica, as they are called here) early in the fourteenth century, Tenochtitlán began on a series of Lake Texcoco islands and expanded for nearly two hundred years as the Aztecs constructed artificial islands and canals for their buildings, plazas, and roads. When the Spanish conquistador Hernán Cortés and his soldiers conquered the city, they immediately set about destroying levees and dikes, draining the Aztecs’ watery world—including Lake Texcoco—and building on the lake bed, sinking wells for drinking water into the aquifer below. That practice has continued in the centuries since, and as the Spanish city has grown in size, it has begun to sink into the old lakebed. On the city’s Main Avenue, at the ornate Palacio de Bellas Artes, all white marble and pillars, visitors step down from street level before climbing the steps to the entrance, and doors that once were at street level are now several feet lower. The city’s statue of El Ángel, the Angel of Independence, built on a hard sediment, has seemed to rise as the surrounding concrete around it has fallen—a century ago, nine steps led from street level to the statue; now there are twenty-three. In some areas of the sinking, city sewer pipes no longer flow outward, and sewage must be continually pumped to keep it from backing up. While the sinking can’t be reversed, it could be slowed or even stopped, but to do so would take billions in investment and, perhaps even less likely, a systematic change in the way the city gets its water.
The problem is that modern Mexico City continues to take some 70 percent of its drinking water from the aquifers below its streets, and at an unsustainable rate. Twice as much water is being taken out as is going in, and scientists say the aquifer is now in danger of collapsing. Zambrano agrees, and worries that if the aquifer suddenly drops, the results could be catastrophic. “So for example,” he tells me, “if in two years we have half the water or one-third the water we are consuming normally—and we are more than twenty million people—you can imagine that would create a huge problem.”
I have come to the university’s central campus, in the southern part of the city, to visit Zambrano at the Reserva Ecológica del Pedregal de San Ángel, the university’s Biological Reserve, 237 hectares of native flora and fauna. A satellite view of the gray city shows two small patches of green at its southern edge. The first is the Biological Reserve. The second is Xochimilco (so-chi-milco), a UNESCO World Heritage Site, a wetland that is all that remains of the rivers and lakes that once served as the setting for Tenochtitlán. The aerial view tells a story of urban sprawl closing in on these last natural areas, the tide of pavement threatening to overwhelm the small remaining islands of what once was.
Standing in the way is Zambrano. Born and raised in Mexico City, Zambrano never imagined he would be where he is today. While around the world the other kids who would grow up to become ecologists played in the woods or fields or lakes near their homes, Zambrano grew up “surrounded by cars.” He was originally drawn to study people rather than nature, and it wasn’t until he started conducting research in Xochimilco that he began, he says, “to feel all the beauty; not understand it, feel it. To see a sunset, or in the early morning when you see all the birds, this is something spiritual.”
As we walk the reserve, Zambrano tells me that even on the university campus, the seemingly inexorable spread of asphalt and concrete threatens this natural beauty. “We have to protect this all the time against everybody,” he says. This despite the fact that already 98 percent of the city’s natural ground is gone. “Now that I am in charge of the reserve, I tell everybody we should stop building. And they say no, it can’t stop.” He sees the city’s failure to contain its growth as a failure to recognize its “carrying capacity,” meaning the maximum population a given environment can sustain with food, water, habitat, and other resources.
“We are like an animal, an organism—and I am an ecologist, so I think all the time in these ways,” Zambrano says with a smile. He explains that every organism, including a human being, has a carrying capacity. Humans are unique in that we can increase our carrying capacity with technology, but eventually, he says, one of two things will happen: “Either we will reach a carrying capacity that even with the most technology we cannot pass through and we will see that no, we can’t grow anymore. That would be…” he pauses, “an optimistic outcome. The other outcome is that our carrying capacity has been expanded by technology a lot, and if the technology fails us, that carrying capacity will drop fast, and then there will be a lot of problems, a lot of deaths.”
Despite what he admits is a sometimes fatalistic point of view, Zambrano is a warm host, full of enthusiasm. When he lectures to faculty and students, PowerPoint images of the city’s growth over the decades draw gasps from his audience, while his regular jokes draw laughs. I see people nodding, listening, paying attention. He’s appealing to common loves—slides of a baby fox, a hummingbird, bats. “Muy bonito,” he says of a particular flower, and everyone in the room agrees, it is very beautiful. With a photo of a resident frog he makes a peep-peep-peep sound. His dress shirt hanging untucked over his khakis, his hair somewhat mussed, his enthusiasm is infectious, as is his love for this small patch of native ground.
He asks rhetorically, Why protect this reserve? For el paisaje, the native landscape, he answers. For the native reptiles, animals, birds—mongoose, owl, salamander. The native plants—yuccas, agaves, and cacti, the complex native systems. Dinámicas complejas. For their sake, yes, and for how they affect Mexico’s people too.
In the past, Zambrano believes, nature gave the various Mexican peoples their identities. Whether it was the Mayans (who thrived between AD 250 and 900), the Olmecs (who carved statues of giant heads from native stone), the Toltecs, or others, they knew who they were because of their relationship with nature. And their nature was specific; different areas had different ecosystems and species. Now, he says, pavement makes nature seem the same everywhere. Cut off from our heritage—the natural ground from which we came, a place our ancestors have known and loved and passed down to us as part of who we are—we lose a piece of ourselves.
In addition to his work here at the reserve, Zambrano’s research focuses on the axolotl, a salamander clinging to existence in nearby Xochimilco. Zambrano tells me of the salamander’s remarkable qualities of regeneration—its ability to regrow legs and spine and arms. But when I see them in his lab I am stunned by their beauty. Each one is a small dark lion, its feathery gills encircling its head like a mane, and with a face that appears curved into a smile. Suddenly I see why the Aztecs saw mythic qualities in this salamander, recognizing in its regenerative ability a metaphor for the way the wetland ecosystem continually sustained their empire. For the Aztecs, axolotls would have been ubiquitous, and even as recently as 1998, the salamander seemed to be holding its own. Since that time, however, its population has crashed. For every sixty counted in 1998, Zambrano says, only one remains today. Their habitat has been drained and paved, their waters clogged with garbage, and an ill-conceived stocking of carp and tilapia has resulted in the destruction of axolotls’ eggs. Today, perhaps only a hundred wild axolotls remain.
Zambrano sees the fate of the salamander and the fate of the Xochimilco ecosystem as inseparable. “It’s like with a tree,” he tells me. “If you cut down the tree, it won’t be only the cutting of this tree but of the relationship between the tree and the nests of the birds, and the seeds, and the roots.” And he sees the inability of his fellow citizens to restrain their city’s constant growth—even at the cost of these last natural grounds, including species like this salamander that once symbolized their ancestors’ civilization—as representative of an urban people cut off from the nature that sustains their life.
Intuitively, we might think, Yes, the environment matters, he explains, but the environment has become an abstraction; it’s hard to connect with because we’re not there anymore, and increasingly isolated from it. “The things that we should be concerned with are actually becoming more foreign and more unfamiliar to us,” he says. This, he tells me, is the worst consequence of all the concrete.
I tell him of my first impression of Mexico City from the air, of how rare the green patches of nature seemed. Looking down from the plane I wondered how far children—or anyone—must have to travel to reach this green. Here in this paved valley, do growing minds imagine this is all there is: a world made by humans for humans as far as the eye can see? Do weeks or months or even whole childhoods pass without hands in the dirt, feet on the grass, ears filled with birdsong or cricket saw or moonlit quiet?
Zambrano nods, and then he tells me about taking his daughter up onto the roof of their house. “In Mexico, things are a little bit dangerous,” he says, between the narco drug-trafficking violence and the impunity with which criminals operate. “At her age, I used to leave the house without any problem and go to the store or even take the bus. I mean, my mother knew I was safe. There were risks, but normal risks. Now, my daughter—she is twelve—wants a lot to go to the park that is in front of our house, and we don’t let her do that because we are really concerned about security.”
We are walking through the Biological Reserve, surrounded by the remnants of the region’s native flora: prickly pear, cholla, yucca—some of Mexico’s nearly one thousand species of cactus, the ground in places black, lava from ancient volcano eruptions.
“One day, last week,” he continues, “it was a very nice evening, at sunset, and I told her, let’s go to the roof because maybe we can see the volcano, because sometimes from the roof you can.” Zambrano is speaking of Popocatépetl, which in the Aztec language means “smoking mountain.” The beautiful snowcapped volcano, forty-some miles south, towers over the city and—if the air pollution isn’t bad or the clouds don’t block it—serves as its backdrop. Zambrano tells me the climb to the roof isn’t easy, that it’s a bit dangerous, and that his daughter had never been there before. When they reached the roof, she smiled.
“She told me, this is nice, and she asked, ‘Could I come to the roof sometimes? Because this will be my way of freeing myself. If I can’t go to the park,’ she said, ‘then let me stay here.’”
Zambrano stops and looks into the distance. “And when she said that, it hit me,” he says, “that as a human she needs to see scenery. It’s not enough to be in the house. She is cut off from nature.”
A few days later, in the Zócalo, the old city’s center square, I myself am feeling cut off from nature. Surely one of the world’s great demonstrations of paving-gone-crazy, the large square has zero green—no trees, no plants, no bushes—just a tall flagpole flying an enormous Mexican flag. This area has been a plaza for centuries, and during Aztec times it was the central market. Bernal Díaz del Castillo, a foot soldier in Cortés’s invading army, wrote, “Among us there were soldiers who had been in many parts of the world, in Constantinople and all of Italy and Rome. Never had they seen a square that compared so well, so orderly and wide, and so full of people as that one.” But around the square the Spanish solders also found evidence of human sacrifice, including a stench of burning human flesh so thick, wrote Díaz, the scene “brought to mind a Castilian slaughterhouse.”
These days the square lies framed by stone government buildings, tourist hotels, and the enormous cathedral built by the Spanish from 1573 to 1813. It’s the cathedral I have come to see—or rather, the ground beneath it, where in 1978 an electrical company crew accidentally discovered the center of the Aztec universe.
The story of the Aztec civilization has long captivated us. Their main city centered around this great square with two pyramids at one end, one of which was the main temple, the Templo Mayor. From 1325 to 1521, the Aztecs built an empire through military conquest and ever-expanding trade. But the empire grew increasingly top-heavy, expanding beyond its means, and by the time Cortés arrived, in 1518, the Aztecs were ripe for a fall. Over the next four hundred years, as the Spanish—and then Mexican—city grew, the old Aztec city lay underneath. Well into the twentieth century, archeologists didn’t know the exact location of the great temple. But since its accidental discovery, more than fifty thousand Aztec objects have been unearthed, many of them exquisite statues and carvings. And the work continues; to visit the Templo Mayor today is to visit an active excavation site.
I visit to meet with Eduardo Matos Moctezuma, who since the 1978 discovery of the Templo has devoted his life to its cultivation. Friendly but reserved, Matos has an eminently authoritative air. In the on-site Museo del Templo Mayor, the wealth of artifacts around us is overwhelming—here a canine skeleton, there a box with thousands of seashells, around the corner an incredible ceramic figure of an eagle, another with the terra cotta shape of a bat (the “original Batman,” he says, smiling). What’s amazing is the way this prehistoric world has emerged from beneath such a solid layer of concrete. It makes you realize what you’re walking over—the cultural history—as you walk Mexico City’s streets. “To break this concrete wall,” he says of the capital’s paved surface, “you’re going down five centuries.” Once, he tells me, a reporter asked him how many archeological sites there are in Mexico, thinking there could be more than a hundred thousand. And Matos told him, “Don’t worry, there’s only one, and it’s called Mexico.”
The Templo Mayor was the Aztecs’ most sacred ground, the place on Earth where the nine levels of the underworld and the nine levels of heaven met. (Anyone familiar with Dante’s fourteenth-century Divine Comedy will know that in his Purgatorio he envisioned nine levels of hell, and in his Paradiso nine levels of heaven. Incredibly, across the world at the same time, the Aztec worldview was remarkably similar.) The Templo Mayor was, Matos explains, “the fundamental center of the Aztec universe, or their cosmovision. It was also the site where the vertical and the horizontal planes met, that is, the passage to the upper or celestial levels and to the underworld, and also the place from which the four directions of the universe departed.” In short, “There is no doubt that the Mexica thus claimed to be the center of the universe, the chosen people.”
That said, the Aztec practice that probably fascinates us most is the custom of human sacrifice. And how can you not be fascinated by accounts like this: “The most significant act in the feast was the sacrifice of a woman who was carried to the top of the temple back to back with a man and beheaded there. Afterward the man was dressed in the skin of the sacrificed woman and in the weaving she had done before her death.” Why was human sacrifice so important for the Aztecs? We might be tempted to see it only as a barbaric act, a mindless waste. In fact, says Matos, “the main goal was to preserve life. You had to give life to preserve life. Most of the human sacrifices were to maintain the movement of the sun, on which all life depended. You had to give blood to the sun.”
In the ritual of human sacrifice, captured soldiers, slaves, or others—often dressed to represent Aztec gods—were brought to the top of the Templo. Their chests were opened and their hearts torn out. (How does that even happen? An artist’s rendering in National Geographic depicts the victim on his back on an altar, soldiers pulling tight on each arm and leg, bloody knives, and a priest holding the dripping heart high over the blood-soaked chest.) Their bodies were then flung down the Templo steps to the plaza below to be dismembered. Matos explains that the Aztecs made human sacrifices to the gods “so that the sun would not stop its course. The gods had to continue to die in order for the universe to continue. A man, converted into a god at the moment of sacrifice, performed what the god did in illo tempore.”
I have to ponder this, imagining those who were to be sacrificed climbing the Templo stairs. Did they understand the role they played? “Absolutely,” he says.
We in the modern West have a hard time grasping the idea of human sacrifice, wanting to consign it to legend, thinking, How could this kind of ritual death happen on such a big scale? But there’s no doubt that these rituals took place. Recent tests of porous surfaces in Mexico City have revealed “blood traces everywhere,” says one archeologist. “You have the sacrificial stones, the sacrificial knives, the bodies of 127 victims—you can’t deny the human sacrifice.”
And “it should be pointed out,” Matos writes in his Life and Death in the Templo Mayor, “that this kind of thinking derived from humans’ observation of everything around them: people, plants, animals, the day. Everything is born and dies, a cycle that is constantly repeated. It is the only way the universe and its renewal can be conceptualized. Everything has to go through the cycle, so there is no belief that people or the sun to which they belong will endure. That would break the pattern of everything created. What has to be maintained is the constant cycle.”
Perhaps sensing my difficulty grappling with this practice, Matos says, “I will say something now that perhaps you do not want to hear. What about your wars in this century, the Germans killing six million Jews, the Americans killing one hundred thousand Japanese with one bomb?” He allows the question to sink in, then says, “And that’s not for life to go on, but for death.”
Paved over often for centuries, this too is something we find in the ground.