The Basilica Ulpia, part of the Forum of Trajan, opened onto its square with three entrances and a façade crowned by an attic decorated with a frieze. The interior was divided longitudinally into five naves and performed commercial and judicial functions. On the shorter sides opened two large apses, into one of which were transferred the functions previously held in the Atrium Libertatis, the seat of the archive of the Censor magistrates and the building where the manumission ceremony was performed, by which slaves obtained their freedom and citizenship, with the attached civil and political rights.

In the late phase of the Roman period we have a series of information indicating the continuity of life of this monument: nineteen laws of the Codex Theodosianus were promulgated in this Forum between 319 and 451 AD. Within the Forum of Trajan, honors were bestowed on the summi viri with the erection of statues, as evidenced by the numerous bases, such as the one found right in the Basilica Ulpia under the Roccagiovine Palace and dated between 440 and 447 CE. This base bears engraved part of an inscription in which Emperor Valentinian III instructs the praefectus urbi to place a gilded bronze statue at that famous site, to honor a living personage whose name has not survived Because of its majesty, the Trajan complex remained in existence much longer than the other great imperial complexes and was destroyed by the earthquake of the year 801, traces of which can be seen within the excavations accessible by FOROF.

The texture of the flooring of the Basilica Ulpia and the alternation of the types of marble, reconstructed thanks to the work carried out, have made it possible to understand how the area of the exedra must in fact have had a texture of rectangular slabs that delimited a series of squares with alternating circles and smaller squares inserted, exactly as must have been the case in the central trunk of the Basilica. The colonnade area had a regular alternation of rectangular slabs of ancient yellow and pavonazzetto placed asymmetrically between them. On either side of the columns, on the other hand, was a band of African green marble. The column bases were inserted into the geometric layout of the floor. Finally, one of the four large roundels that must have been placed at the apexes of the two outermost aisles was brought to light, perfectly preserved.