Emperor Augustus built another forum close to the one of Caesar. It was larger and was protected by a high wall. In the centre was a Temple of Mars Ultor (the Avenger), which Augustus promised to erect during a battle with Philipps in 42 b.C. revenging the death of Caesar. It stood on a basement 3.5meters high with the steps preceding it. The temple had eight Corinthian columns on each side, and apse with the statues of Marte and of Venice. On either side of the temple were twin basilicas which were almost completely destroyed during the Renaissance for their marble.

The left-hand basilica had an extension at the north end known as the Hall of the Colossus, a square room which held a colossal statue of Augustus or of Mars (its basement survived). Here was also a series of statues of principal generals of the Roman army. The Arch of Pantanus served as the entrance to the forum. Political and religious ceremonies (nomination of the governors of the provinces, etc.) took place here.

The construction of the Forum of Augustus was completed only a century later by other emperors.

In the Middle Ages it was occupied by a convent of Basilians and the temple was turned into a Chiesa di S.Basilio with the added Romanesque bell-tower. Later the monastery passed to the nuns Dominicans and the new church was created: Chiesa della Annunziata (it was demolished in the 30's of the 20th century in course of excavation of the Forum of Augustus).