Boulogne-sur-Mer, often called Boulogne, 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 tourist 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 60th largest in France. It is also the country's largest fishing port, specialising in herring.
Boulogne was the major Roman port for trade and communication with Britain. After a period of Germanic presence following the collapse of the Empire, Boulogne was at the centre of the County of Boulogne 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. In 1805 it was a staging area for Napoleon's troops for several months during his planned invasion of the United Kingdom.
The city's 12th-century belfry is recognised by UNESCO as a World Heritage Site, while another popular attraction is the marine conservation centre Nausicaa.