By coming of the Empire and by increasing of population, commerce, diplomacy, celebrating monuments made built by emperors, the old forum was not sufficient anymore to host the new buildings and the forum grew around some new squares built by Caesar, Augustus, Trajan, Nerva and Vespasian, enlarged and enriched by other emperors.

Nowadays remain few testimonies of the originary richness and magnificence of Imperial Forums. In the Trajan Forum: the Trajan Column, on which there is a continuous bas-reliefs spiraling up with more than one hundred distinct scenes representing the victory of Trajan upon Daci; on its top there was the bronze statue of the emperor, replaced in XVI century by a statue of St.Peter.

In the Forum of August: the Temple of Mars, of which remain some columns, the entrance stairway and part of surrounding walls, upon which was built the House of Knights from Rodi in the Middle Ages. In the Forum of Caesar: the Temple of Venus Genitrix, of which remains nowadays only some columns.

In the Trajan Forum was built also the new imposive seat of the general markets, called Trajan Markets, planned by the great architect Apollodoro from Damascus and consisting of more than 150 stores on several floors on the slope of Quirinale. Nowadays they host the Museums of Imperial Forums, exhibiting remains collected during the excavation works.