The Arch of janus was difficult to locate betwen the forum Boarium and the Velabro.

With a length of 12 m and a height of 16 m the Arch of Janus was standing in the Velabro towards the forum Boarium. It might have been erected in the honour of the Emperor Constantine II around 356 AD.

The Arch of Janus was on the communication ways of the Velabro. On the map, you can notice the double blue line going under the Arch of Janus. It is the identification of the great sewer (cloaca maxima) which stretched between the Capitol, the Palatine and the slopes of the Esquiline. The Cloaca Maxima allowed to drain the swampy valley. Still today you can see the outlet of the sewer on the side of the Tiber.