The Arch of Constantine is a triumphal arch, erected c. 315 CE to commemorate the triumph of Constantine I after his victory over Maxentius in the battle at the Milvian Bridge in 312 CE. The arch is located in the valley of the Colosseum, between the Palatine Hill and the Colosseum, along the road taken by the triumphal processions.

The arch is the largest of only three such arches to survive in Rome today. The two others are the Arch of Titus and the Arch of Septimius Severus, both in the nearby Forum Romanum.

The battle of the Milvian Bridge in 312 CE was the decisive moment in Constantine's quest for power. He had been proclaimed Augustus by the troops in Britain in 306 CE, after the death of his father in York, and even though he had no legal right to that title, he refused to relinquish it. Likewise, Maxentius claimed the title of Augustus of the western empire. The conflict was finally resolved in the battle of the Milvian Bridge just N. of Rome, when Constantine's army defeated the numerically superior but less experienced troops of Maxentius.

Constantine entered Rome victoriously, and the senate awarded him a triumphal arch. Construction began immediately, and the arch was finished in a few years, to be consecrated in 315/316 CE on the tenth anniversary of Constantine's rise to power.