Bononia is generally identified with the Boulogne. The name derives from a gaulish root bun " low". Bononia is then perhaps "the low place". This name is coupled with Gesoriacum meaning "the place at the point" that seems to have been used interchangeably with Bononia. The point could have been Cap Gris Nez or the small headland closer in, called today Le Portel.

Alternatively gesor, "pointed" could refer to Boulogne's upper town, built on a pointed spur, leaving Bononia for the lower town. Bononia replaced Gesoriacum in the Peutinger Table and developed naturally following French phonetic rules into Boulogne. Julius Caesar used the port for his two expeditions to Britain (55 and 54 BCE) but refers to it as Portus Itus.