Boulogne-sur-Mer (bōlôˈnyə-sür-mĕrˈ) [key], city (1990 pop. 44,244), Pas-de-Calais dept., N France, in Picardy, on the English Channel. A commercial seaport and the leading fishing port of France, it has canning and shipbuilding industries. It is an important ferry port between France and England. The opening of the Channel Tunnel at nearby Coquelles, France may have an impact on the city's ferry services and industries. From there the Romans sailed (A.D. 43) to conquer Britain, and there again Napoleon assembled an invasion fleet (which never sailed) in 1803–5. The port was a main base for British armies in World War I and a German submarine base in World War II. Most of the city was destroyed during the latter conflict. The Cathedral of Notre Dame (built 19th cent.; damaged 1941; since restored) is a great shrine of pilgrimage; it stands on a site where miracles were believed to have occurred in the 7th cent.