Boulogne-sur-Mer (46), a fortified seaport in France, on the English Channel, in the dep. of Pas-de-Calais, 27 m. SW. of Calais, one of the principal ports for debarkation from England; where Napoleon collected in 1803 a flotilla to invade England; is connected by steamer with Folkestone, and a favourite watering-place; the chief station of the North Sea fisheries; is the centre of an important coasting trade, and likely to become a naval station.