Château de la Tournelle

The Château de la Tournelle, which once stood on the banks of the Seine in the fifth arrondissement, was a square fortress named for the small towers, or tournelles, that monitored the river. Built during the reign of Charles the Sixth, the structure replaced an older watch tower from the thirteenth-century wall of Philippe Auguste. While it initially served a military role to protect Paris from riverborne invasion, it is best remembered for a later, grim chapter in its history.