Although this 4 sided arch is named after Arch of Janus, the god with 2 heads looking in opposite directions, it was probably an honorary tribute to the Emperor Constantine and was erected in the most easterly part of the Forum Boarium, the cattle market, in the area known as Velabrum.

As well as being a monument, the arch provided shelter to the merchants during their business deals and negotiations.
At the back of this arch you'll find the Church of San Giorgio in Velabro, a parish church of the 5^th century.
Velabrum was the ancient name given to the marshy ground beside the river; it was here that Faustolus found the twins Romulus and Remus in a floating basket. The basket had been snared by the roots of a fig tree on the bank of the Tiber. The area is one of the most symbolic of the legends that narrate the story of the birth of Rome.