To build this monumental complex, extensive excavations were required: workers eliminated the sides of the Quirinal and Capitoline Hills, which closed the valley occupied by the Imperial forums toward the Campus Martius.

It is possible that the excavations were initiated under Emperor Domitian, while the project of the Forum was completely attributed to the architect Apollodorus of Damascus,who also accompanied Emperor Trajan in the Dacian campaign.

During the time of the construction, several other projects took place: The Markets of Trajan were constructed, Caesar's Forum, where the Basilica Argentaria was built, and the Temple of Venus Genetrix were renovated.