Arch of Constantine

After years of civil war, the victory of Constantine's army over the numerically superior army of Maxentius at the Battle of Milvian Bridge in 312 AD brought some peace to the Roman empire.
To commemorate this victory, the Senate of Rome awarded Constantine a Triumphal arch. It was dedicated just a few years later, in 315 AD.

The large arch with 3 archways is almost 26m (85ft) wide and 21m (69ft) high. During construction, many parts from older structures were reused, which was common practice at the time.
The statues at the top were taken from the Forum of Trajan. They depict Dacian captured soldiers, defeated by the Trajan army.
The reliefs between the statues were created for Marcus Aurelius while the roundrels (and possibly even the arch itself) are from emperor Hadrian's time. Some figures in the roundrels were modified to resemble Constantine. The decorations at the central and lower part were created specifically for this triumphal arch.

During Constantine's reign, persecution of Christians ended and Christianity became the official religion in the Roman empire. He also moved the capital of the empire from Rome to Constantinople in 325 AD (before known as Byzantium, now Istanbul).