How the Million-Strong City of Rome Was Successfully Supplied with Fresh Water

The Roman politician Appius Claudius Caecus — the same one who built the Appian Way — also distinguished himself by constructing the first large aqueduct that supplied the city of Rome with water. By the end of the 4th century BCE, Rome had already become a large city, and drawing water directly from the Tiber River was becoming increasingly difficult for its inhabitants. Moreover, the water in this river was far from clean, which negatively affected public health. Appius proposed building a water conduit (exactly what the Latin term aquae ductus translates to) that would supply Romans with spring water.

The above-ground section of the Aqua Appia in modern times

For almost its entire length, the pipes of the Aqua Appia run underground, but within the city, in the area between the Caelian and Aventine Hills, they emerge to the surface. The ancient Romans understood the principle of communicating vessels and used it in their water supply systems. So why are most Roman aqueducts above-ground structures of enormous length, the construction of which required vast quantities of building materials and labor? The reason is that when water flowed by gravity at a constant gentle slope, it did not create high pressure on the aqueduct’s pipe walls. As a result, these aqueducts remained functional for a long time with minimal maintenance.