Boulogne-sur-Mer (bulɔɲ syʁ mɛʁ; Boulonne-su-Mér; Bonen; Gesoriacum or Bononia), often called just Boulogne (UKbʊˈlɔɪn, USbuːˈloʊn,_buːˈlɔɪn), is a coastal 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 stretch of French coast on the English Channel between Calais and Normandy, and the most visited location in the region after the Lille conurbation. Boulogne is its department's second-largest city after Calais, and the 183rd-largest in France. It is also the country's largest fishing port, specialising in herring.
Boulogne is an ancient town and was the main Roman port for trade and communication with its Province of Britain. After a period of Germanic presence following the collapse of the Empire, Boulogne was integrated into the County of Boulogne of the Kingdom of France during the Middle Ages. It was occupied by the Kingdom of England numerous times due to conflict between the two nations. In 1805