Solidor Tower (in French tour Solidor) is a strengthened keep with three linked towers, located in the estuary of the river Rance in Brittany. It was built between 1369 and 1382 by John V, Duke of Brittany (i.e. Jean IV in French) to control access to the Rance at a time when the city of Saint-Malo did not recognize his authority. Over the centuries the tower lost its military interest and became a jail. It is now a museum celebrating Breton sailors exploring Cape Horn. The Solidor Tower is located in the former city of Saint-Servan, which merged with Saint-Malo in 1967.