The four-sided structure known as the Arch of Janus in the Forum Transitorium dates from the 1st century of the Christian era: according to common opinion it was built by the Emperor Domitian. However American scholars L. Ross Taylor and L. Adams Holland on the grounds of a passage of Statius maintain that it was an earlier structure (tradition has it the "Ianus Quadrifrons" was brought to Rome from Falerii) and that Domitian only surrounded it with his new forum. In fact the building of the Forum Transitorium was completed and inaugurated by Nerva in AD 96.