The arch of Janus is the only quadrifrons triumphal arch preserved in Rome and is one of the principal monuments in the Forum Boarium in the Valabrum. It is the only triumphal arch with four front sides. It was built in the early fourth century of marble from earlier buildings, possibly in honour of Constantine I, the name being derived from its four-fronted, four-arched structure. The building survived intact until 1830 when the attic and top were torn down because they were erroneously believed not to belong to the original structure. A micromosaic depicting the same subject and attributed to Giacomo Raffaelli (1753-1836) is illustrated in J. H. Gabriel, The Gilbert Collection of Micromosaics, London, 2000, p. 59.