Boulogne-sur-Mer is a city in northern France. It is a sub-prefecture of the department of Pas-de-Calais.The name Boulogne was first recorded during the Roman Empire as Bononia, possibly a derivative of the root found in the Germanic word bona meaning "plank floor", related to "Buhne", German for theater stage and also found in Vindobona, the Roman name for Vienna. A "bona" was probably a granary. This derivation is also found in the name of the Italian city of Bologna. This city was founded by the celtic Boii. "Sur mer" is French meaning "on the sea".
Originally named Gesoriacum and probably also to be identified with Portus Itius, by the 4th century Boulogne was known to the Romans as Bononia and served as the major port connecting the rest of the empire to Britain. The emperor Claudius used this town as his base for the Roman invasion of Britain, in AD 43, and until 296 it was the base of the Classis Britannica.