The Cloaca Circi Maximi or Cloaca Circi was a sewer in ancient Rome.
It was originally a small stream fed by various sources from around the Porta Capena right through the valley between the Palatine Hill and Aventine Hill, running down to the river Tiber. According to tradition, games and horse races were held in this vallery from right after the founding of Rome in the 8th century. Over the centuries the Circus Maximus was built over the stream, with a channel named Euripus running across it halfway and two bridges carrying the track over it. The channel also served as the spina down the middle of the track.
Under Julius Caesar and Augustus the circus and its surroundings were greatly enlarged, covering over the channel, which became a sewer. It was connected to a tunnel modelled on that of the Cloaca Maxima and now terminated on the Tiber upstream of the Cloaca Maxima.