Boulogne-sur-Mer (Latin: Bononia) is a city in northern France. It is a sub-prefecture of the department of Pas-de-Calais. Boulogne lies on the Côte d'Opale, a touristic coast on the English Channel, and is the most-visited location in its region after the Lille conurbation. Boulogne is its department's second-largest city after Calais, and the 59th largest in France. It is also the country's largest fishing port, specialising in herring.
Boulogne was founded during the Roman occupation of France, and as Portus Itius, was used for trade and conquest of Great Britain. After a period of Germanic presence following the collapse of the Empire, Boulogne was at the centre of an eponymous county of the Kingdom of France during the Middle Ages, and was occupied by the Kingdom of England numerous times due to conflict between the two nations.