Aqueducts are some of the best known Roman architectural works. They were used to carry water around the Roman Empire, and some remain in use in the modern world.
The first Roman aqueduct was built around 312 B.C.; the last, the Aqua Alexandrina, in 226 A.D. During the 500-year period of Roman aqueduct building, 11 aqueducts in Rome (population of about a million) stretched for 359 miles and provided 50 million gallons of water on a daily basis.
Roman aqueducts were built to operate using gravity. The aqueduct tunnels were built at ground level and underground, at a slight 1/200 slope, to keep water flowing by gravity.
When the aqueduct had to run through a valley, sometimes closed pipes were used instead of tunnels. The water was transported using the inverted siphon method which forces water from higher ground to lower terrain back up to higher terrain using the pressure of the water.
Aqueducts allowed fresh water to be transported to cities and towns for drinking, irrigation and sanitation purposes. This allowed the Romans to build large cities in areas such as dry plains.
According to Peter Aicher, associate professor of Classics at the University of Southern Maine, Rome had water connoisseurs who ranked the aqueducts. Aqua Marcia (one of the longer aqueducts) and Aqua Virgo (feeds the Trevi fountain in modern times) were the top-ranked aqueducts.