sentences:  Built to the same height, the roofs of the towers and the tops of the walls formed a broad, crenellated walkway all the way around the fortress.Each of the six newer towers had underground "cachots", or dungeons, at its base, and curved "calotte", literally "shell", rooms in their roofs.Garrisoned by a captain, a knight, eight squires and ten crossbowmen, the Bastille was encircled with ditches fed by the River Seine, and faced with stone.