tetrapylon

thumb|The North Tetrapylon at Jerash in Jordan

A tetrapylon (plural tetrapyla; ; , also used in English) is a rectangular form of monument with arched passages in two directions, at right angles, generally built on a crossroads. They appear in ancient Roman architecture, usually as a form of the Roman triumphal arch at significant crossroads or geographical "focal points". thumb|alt=The so-called "Arch of Janus" in Rome|The so-called "Arch of Janus" in Rome, 4th-century