The name literally meaning "Great Sewer", the Cloaca Maxima was one of the world's first major sewage systems. Records suggest it was built as early as 600 B.C.E. under order of King Tarquinius of Rome. Aside from taking sewage away from the city, it's widely accepted that the Cloaca was used to drain the once swampy location of the Roman Forum.
Surprisingly, it still remains in use today as a drainage system for excess rain water.
I bet you thought I would make a sewer joke, huh? Please. Too easy.