Called Brigantium in Roman times, Briançon had an antique agglomeration of 62 acres (25 ha) whose location corresponded to the Champ de Mars sector. The Gallo-Roman remains of a tower still rising are preserved in the embankment of the southern fortifications of the 17th century. They suggest the existence of an important defensive system delimiting the urban space at the end of the 3rd century or the beginning of the 4th century.