From former discoveries we know that, on its north-east and north-west sides, the rectangular medieval wall of the Upper Town at Boulogne-sur-Mer hides a Later Roman Empire rampart. Recent diggings have uncovered a military camp of the Classis Britannica settled in the Upper Town during the High Empire. Excavations in rue Saint- Jean enabled us to find out that the three successive walls from the High Empire, the Later Empire and the Middle Ages are parallel, and built from the inside to the outside. From other evidences we can conclude that it was probably the same on the three other sides of the medieval rampart quadrangle, which had four gates, one in the middle of each small side, one at the quarter of the length of the long sides. The ...