The Arch of Janus is a tetrapylon triumphal arch, also known as a quadrifron. It’s the only remaining structure of its kind in Rome.
It’s located at the edges of the Forum Boarium, a market area of ancient Rome. The arch was constructed during the 4th-century using materials from older buildings in the city. It’s known as the Arch of Janus but has nothing to do with the Roman god of gates. The arch was never given this name during antiquity. The name likely came from the Latin word ianus during the Renaissance period and derived from its four-fronted, four-arched configuration.
About the source: Atlas Obscura
Atlas Obscura aims 'to inspire wonder and curiosity about the incredible world we all share'. You can contribute to their collection on their website.