c. 800 BCE

Aqueducts

The invention of agriculture and thus of settled, agrarian societies led inexorably to the growth of cities. Large population centers require large supplies of food and water to remain sustainable. As population continues to grow, however, local supplies of these resources might not prove adequate, meaning that food and water would have to be imported to sustain a city.

Bringing water into a city (or farming community) presents special additional engineering and logistical challenges compared to importing food. In many desert or plains environments, it was possible for people to dig canals to divert water from rivers into settlements, even back in prehistoric times. However, in areas of rugged topography, excavating canals might prove impractical or impossible. Hence the idea emerged, perhaps as long as 4,000 years ago according to some archaeological evidence, to connect canals and other waterways by water-bearing bridges—known as aqueducts—where the terrain required them. Perhaps the most famous of the early aqueducts known to historians was a 50-mile (80-kilometer) aqueduct made of limestone built by the Assyrian empire in Mesopotamia about 2,800 years ago, which included a water bridge about 30 feet high (10 meters) and about 1,000 feet long (300 meters) across a valley. Ruins of this monumental engineering achievement remain today in the region around Jerwan in northern Iraq.

Centuries later, the Romans would expand on these older designs and deploy a massive system of hundreds of canals and aqueducts to supply water to farms, towns, and cities across the Empire. Rome itself had eleven aqueducts by the third century, helping to sustain a population of over a million people. Some of the imported water fueled an extravagant water-rich lifestyle of fountains and public baths for the wealthy and noble; but just as importantly, some was also used to power water mills, and some to attempt to maintain higher standards of general public health by flushing sewers and drains.

Sections of many Roman aqueducts are still preserved today, and a few are still in partial use. More generally, aqueduct designs and building methods were widely mimicked in Roman and subsequent architecture, and the concept of an elevated water bridge is even in use today in some places where canals and lock systems encounter topographic obstacles.

A well-preserved ancient Roman aqueduct in Segovia, Spain, thought to date from the late first to early second centuries CE.