Arch of Janus

The Arch of Janus in the Forum Boarium is the only surviving quadrifrons arch in Rome. This arch with four facades marked an important meeting place and crossroads in antiquity, where a busy port on the Tiber River met the slope of the Palatine Hill and led into the heart of the ancient city. Contrary to popular belief, the arch was not dedicated to the Roman god Janus, but it was named after the Latin word ianua, or door, which was itself derived from the name of the double-headed god of beginnings and transitions. The arch rests firmly on four broad pillars that support a cross vault. 

The structure is covered with marble slabs taken from the ruins of earlier buildings, and this construction technique has helped archaeologists date the structure to the second half of the fourth century. The keystones on each of the four sides are decorated with figures of Rome and goddesses of the Roman pantheon, while niches on the outward-facing sides of the four pillars contained other statues, now missing. Originally the arch supported a penthouse, which was removed in the nineteenth century, when it was mistaken for a medieval accretion, giving the arch the stout look that it has today.