What famous arch is located just east of the Colosseum?

The famous arch located just east of the Colosseum is the Arch of Constantine.

This triumphal arch stands between the Colosseum and the Palatine Hill, along the ancient route used by victorious Roman commanders. The Roman Senate dedicated it to Constantine the Great after his victory over Maxentius at the Battle of the Milvian Bridge in AD 312. It was dedicated in AD 315, also celebrating Constantine’s decennalia, or tenth anniversary of rule.

The arch has three passageways and is about 21 metres high. Its decoration is historically unusual: many reliefs and statues were taken from monuments associated with earlier emperors, including Trajan, Hadrian, and Marcus Aurelius, then adapted for Constantine.

It is easy to confuse this monument with the nearby Arch of Titus, which stands along the route toward the Roman Forum. The Arch of Septimius Severus is also in Rome, but it is located in the Roman Forum rather than beside the Colosseum.