The so-called Basilica is a hall (c. 14.50 x 11.30) that could be accessed from the Decumanus Maximus. It was excavated during the First World War by Roberto Paribeni. The walls are of Hadrianic opus latericium (c. 120 AD).

The hall is divided into two naves by brick piers. The left nave is wider and has an apsidal wall of opus mixtum at the north end (w. 3.60, d. 1.70). To the left of this nave is a corridor, with a door in the north wall. There is a door at the north end of the right nave as well. Several modifications took place: passages in the east wall of the right nave were blocked (opus latericium); a few brick piers were added in the north part of the left nave; the entrance of the left nave from the Decumanus (6.35 m. wide) was narrowed and decorated with a porch; in the left nave a rectangular masonry basin was added. The north wall with the apse and the additional piers have been dated to the second half of the third century. The narrowing of the main entrance and the latericium of the east wall have been dated to the years 350-375 AD. To the north-east are two rooms, a latrine and a staircase, to the north-west is the Hall of the Good Shepherd (I,II,4).

In the building an inscribed marble plaque (0.19 x 0.25 m.) was found in 1951. It was erected during the reign of Gordianus III (238-244 AD) by the guild of the lenuncularii traiectus Luculli, a ferry-service on the Tiber. The "Basilica" or the Hall of the Good Shepherd to the north may have been the seat of this guild.

IMP(eratori) CAES(ari) M(arco) ANTO NIO GORDIANO PIO FELICI AVG(usto) CORP(us) TR(aiectus) LVCVL(li)	To the Emperor Caesar Marcus Antonius Gordianus, pious, happy, Augustus, the guild of Lucullus' Crossing.
EDR080297.

Also from this building comes a marble slab with a dedication to Publius Aufidius Fortis, patron of the colony:

P(ublio) AVFIDIO P(ubli) FIL(io) QVIR(ina) FORTI AVFIDI FORTIS P(atroni) C(oloniae) FIL(io) IIVIR(o) Q(uaestori) AEDIL(i) FLAM(ini) ROMAE ET AVG(usti) FLAM(ini) DIVI TITI FAVSTIANVS EPICTETVS EVPHROSYNVS IANVARIVS LIBERTI	To Publius Aufidius Fortis of the tribe Quirina, son of Publius Aufidius Fortis, patron of the colony, mayor, quaestor, aedile, priest of Roma and Augustus, priest of the deified Titus, Faustianus, Epictetus, Euphrosynus, Ianuarius, his freedmen.
EDR072773. 131-170 AD.