The Digue de Richelieu is a dam, exposed at low tide, built by Cardinal Richelieu during his successful siege of the city in 1627-28, during the wars of the Reformation. The dam constricts the entrance to the harbor to a width of about 100 m. The north side of the entrance was long marked by a succession of wooden daybeacons. The original Tourelle Richelieu, a round stone tower, replaced these beacons in 1863, but it was destroyed when a fishing trawler ran it over on January 21, 1914. The present tower was modified in 1955 to include an octagonal room at the top housing a radiobeacon and fog signal (neither of which remains in use today).

ARLHS Number: FRA-518
Admirality Number: D1250
NGA Number: 1380
Build: 1915
Construction: concrete
Height: +/- 10 m
GPS: 46 08 53 / -1 10 20