It is one of the most enormous arches ever built in Rome. It is 21 metres high, almost 36 metres wide and its walls are over 7 metres thick. The arch was built in 315 by decree of the Senate and the Roman people to celebrate the tenth anniversary of Constantine's reign and the victory he won in 312 at the Battle of Ponte Milvio against Maxentius. Many bas-reliefs and sculptures removed from other monuments were used to decorate this arch. On both of the large pillars of the arch are four columns dating back to the reign of Trajan; above the columns are eight statues of Dacians made of white marble of Asia Minor with purple veins.
Above the side arches are eight medallions of Hadrian's time, grouped two above each arch. Four of the scenes depicted in them reproduce hunting scenes, the other four scenes are of sacrifice. On either side of the inscription, repeated on two ribbons of the attic, one can see eight bas-reliefs from the Marcus Aurelius period, which once adorned another triumphal arch and are also placed two on each side. The bas-reliefs depict the solemn moment of the "Return of the Emperor" in 173 after the victorious battles with the Germanic tribes of the Marcomanni and Quadians. The large marble frieze from Trajan's era is also a borrowing. It is divided into four parts: two fragments are placed above the small arches and two inside the central span. The sculptural reliefs reproduce scenes of Trajan's military campaigns against the Dacians (101-102 and 105-106).
