The discovery of early Gallo-Roman objects on the site of the forum, as well as the vestiges of houses aligned with the cardo of the Boulevard Saint-Michel appear to indicate that the forum occupied a space that was not originally reserved for it in the urban grid.

Items recently discovered in occupation layers predating the forum's construction suggest that it was founded in the second half of the 1st century BCE, sometime between the reigns of Claudius (41-54) and Vespasian (69-79). The plan of the building, as far as can be currently established, seems to indicate that it was designed and built in one go.

  It is impossible to find any core area of the forum that underwent subsequent modifications. Nevertheless, we cannot rule out the fact that the building was embellished, renovated and reworked from time to time-certain architectural elements can be dated to the 2nd century CE.

As for its abandonment, we know that the building served as a stone-quarry for Late Empire buildings and ramparts, but there is no indication that the building completely disappeared at this time.