Rome's sewer system.
Circa 600 B.C.E.
The Cloaca Maxima was one of the world's first major sewage systems. Records suggest it was first built as early as 600 B.C.E. under order of King Tarquinius of Rome. Aside from taking sewage away from the city, it is widely accepted that the Cloaca was used to drain the once swampy location of the Roman Forum.