The Arch of Constantine is a triumphal arch in Rome dedicated to the emperor Constantine the Great. The arch was commissioned by the Roman Senate to commemorate Constantine's victory over Maxentius at the Battle of the Milvian Bridge in AD 312. Situated between the Colosseum and the Palatine Hill, the arch spans the Via Triumphalis, the route taken by victorious military leaders when they entered the city in a triumphal procession. [a] Dedicated in 315, it is the largest Roman triumphal arch, with overall dimensions of 21 m (69 ft) high, 25.9 m (85 ft) wide and 7.4 m (24 ft) deep. It has three bays, the central one being 11.5 m (38 ft) high and 6.5 m (21 ft) wide and the laterals 7.4 m (24 ft) by 3.4 m (11 ft) each. The arch is constructed of brick-faced concrete covered in marble.

Though dedicated to Constantine, much of the sculptural decoration consists of reliefs and statues removed from earlier triumphal monuments dedicated to Trajan (98–117), Hadrian (117–138) and Marcus Aurelius (161–180), with the portrait heads replaced with his own.

The location, between the Palatine Hill and the Caelian Hill, spanned the ancient route of Roman triumphs (Via triumphalis) at its origin, where it diverged from the Via Sacra. This route was that taken by the emperors when they entered the city in triumph. This route started at the Campus Martius, led through the Circus Maximus, and around the Palatine Hill; immediately after the Arch of Constantine, the procession would turn left at the Meta Sudans and march along the Via sacra to the Forum Romanum and on to the Capitoline Hill, passing through both the Arches of Titus and Septimius Severus.

There has been much controversy over the origins of the arch, with some scholars claiming that it should no longer be referred to as Constantine's arch, but is in fact an earlier work from the time of Hadrian, reworked during Constantine's reign,[4] or at least the lower part.[d] Another theory holds that it was erected, or at least started, by Maxentius, and one scholar believed it was as early as the time of Domitian (81–96).

Whatever the faults of Maxentius, his reputation in Rome was influenced by his contributions to public building. By the time of his accession in 306 Rome was becoming increasingly irrelevant to the governance of the empire, most emperors choosing to live elsewhere and focusing on defending the fragile boundaries, where they frequently founded new cities.

en.wikipedia.org