The final Imperial Forum
Trajan's Forum was the final Imperial forum built in Rome. It's located near the Piazza Venezia and the monument to Vittorio Emmanuel III. It was built by the Emperor Trajan and is known for the massive column built in memory of his conquests in Dacia. To create this awe-inspiring forum, the Romans had to level two nearby hills, the Quirinale and the Campodoglio. All Imperial Forums are relatively close together and you can visit them at the same time that you visit the Colosseum.
At the same time, the Trajan Market was built on what was the Forum of Caesar. The forum is a large square lined with porticoes with the Basilica Ulpia with its statue of the Emperor on his horse toward the bottom. The ruins themselves make this a worthy visit. I'd especially recommend visiting at night when everything is lit up.


