Standing beside the Colosseum, Constantine's triumphal arch was one of the last great Roman monuments, erected in AD 315, shortly before the emperor abandoned the city for Byzantium. Built to commemorate the Battle of the Milvian Bridge, Constantine's is the best preserved of Rome's triumphal arches. Its magnificent relief sculptures and statues were almost all lifted from earlier emperors' monuments around the city; those panels that are Constantinian (the narrow strips above the side arches, for example) give ample evidence of the decline in realism of late antique sculpture, as well as the dearth of skilled artisans and workers.
In front of the arch, the round foundation sunk in the grass is all that remains of an ancient fountain called the Meta sudans ('sweating cone'). Much more of this implausibly phallic object - almost all of it, in fact - would have been visible today if it hadn't been for Mussolini's avid bulldozing in the 1930s.