The Arch of Constantine (Latin Arcus Constantini, Italian Arco di Costantino) is a triple triumphal arch located along the route of the triumphal procession between the Roman Forum (Forum Romanum) and the Colosseum. Completed around 315, it was erected to honor Constantine’s victory over Maxentius at the Milvian Bridge in 312 – and at the same time to celebrate his decennalia. The Constantinian reliefs on the arch are commonly held to mark a shift in art, while it is also noteworthy for its extensive use of spolia – reused reliefs from the second century CE.

This triple arch is similar in size and design to the Arch of Septimius Severus in the Roman Forum built a century earlier. It is over 25 meters wide and 21 meters high and has a large inscription above the central passage proclaiming Constantine as the liberator of Rome. Eight columns with Corinthian capitals on the façade rest on plinths decorated with captives, soldiers, and the personifications of victory (Victoria) from the Constantinian era. A narrow frieze runs around the arch above the small arches with scenes of the recent activities of Constantine. These reliefs depict (running from east to west) the March to Verona, the Siege of Verona, the Battle of the Milvian Bridge, the Entrance to Rome, Imperial Oration from the Rostra at the Roman Forum, and the Distribution of Money. Other reliefs from the Constantinian era include depictions of the sun and the moon in roundels on the ends of each arch, and personifications of the seasons, river gods, and victory in the spandrels.

Among its spolia are reliefs from monuments originally dedicated to Trajan, Hadrian, and Marcus Aurelius – often with their heads recut. Above the small arches are eight Hadrianic roundels showing, for example, hunting and sacrifice scenes. The Trajanic reliefs, located inside the passageway of the central arch and at the end of the attic, depict battles between Romans and Dacians. Several large free-standing Trajanic statues depicting Dacian captives are located on the attic. There are also eight panels of high relief sculpture of Marcus Aurelius on the attic, depicting the emperor at war and engaged in hunting and sacrifice scenes. While the decorative program celebrates imperial authority and victory as is typical for triumphal arches, it has also been read as Constantine's appropriation of the earlier imperial achievements.