Ancient Engineering: How Roman Aqueducts Defied Gravity to Move Water Uphill

Aqueducts remain among the most iconic remnants of ancient Roman civilization, primarily relying on gravity to slowly channel water into urban centers. However, certain structures, such as the second-century A.D. aqueduct in Aspendos, Turkey, required water to travel upward. According to experts speaking to Live Science, Roman engineers employed a variety of techniques, including inverted siphons and mechanical water-lifting devices, to overcome these topographical challenges.

One primary solution was the inverted siphon system. Virtual modeling simulations of the Aspendos aqueduct reveal how Roman engineers navigated valleys. They constructed a large “header tank” at the entrance of a valley and a slightly lower “receiving tank” on the opposite side. Between these tanks, two towers were erected. As water descended a steep slope, the resulting pressure forced it up the first tower, down the other side, and then up the second tower before reaching the outlet tank, allowing the flow to continue toward the city.

Preventing air pockets was critical for the success of these siphons. Giovanni De Feo, a professor of industrial engineering at the University of Salerno, explained that the substantial size of the header and receiving tanks allowed air bubbles to rise naturally to the surface and escape through the open tops. The larger chamber volume decreased water velocity, thereby reducing the risk of air locks forming within the system.

Despite the effectiveness of siphons, Roman engineers often preferred alternative methods when possible. Charles Ortloff, a research associate in the Department of Anthropology at the University of Chicago, noted that engineers typically favored building elevated bridges with top channels to cross valleys rather than using siphons. The famous Segovia aqueduct in Spain stands as a surviving example of this bridge-based approach.

Beyond siphons, the Romans utilized various devices to elevate water. The Archimedes screw, attributed to the third-century B.C. Greek inventor though possibly invented earlier, was commonly used to lift water from rivers to fields. Operated by animal power, the device featured a wooden shaft wrapped with flexible willow or wicker branches, creating an endless screw inside a wooden pipe. Positioned at a 30-degree angle in the water, rotation of the screw lifted the water to higher ground.

Water wheels were also instrumental, particularly in mining operations. These large, carriage-wheel-like devices featured buckets attached to their circumference to catch and raise water. Additionally, the Romans employed Ctesibius’ pump, a hand-operated device consisting of two cylinders connected to a central chamber by pistons, which expelled water through a nozzle. These innovations ensured that uphill gradients never halted the delivery of water to Roman destinations.