Solidor Tower, Medieval keep in Saint-Servan district, Saint-Malo, France

Solidor Tower is a medieval fortification in Saint-Servan built from granite with three connected circular towers rising over multiple stories. The thick walls and narrow windows show how it was designed as a military stronghold overlooking the Rance estuary.

John IV, Duke of Brittany, built the keep between 1369 and 1382 to control the Rance while Saint-Malo refused his authority; a Latin record of the time calls it Stiridort, from Breton for "river gate". It replaced an earlier tower, the Tour d'Oreigle, itself set on 4th-century Gallo-Roman defences of the port of Alet. In 1756 the drawbridge was replaced by a stone bridge, and in 1886 Albert Ballu restored the tower and gave it its present roof.

The tower once housed a museum celebrating Breton sailors who rounded Cape Horn, with displays of ships and navigation tools from their journeys. Those exhibitions told stories of dangerous voyages and the courage of local mariners who ventured across distant oceans.

The tower stands on a rocky point at the mouth of the Rance, in the Saint-Servan district; the Solidor slipway beside it was the departure point for the ferry to Dinard until the Rance tidal power station opened in 1967. The tower itself has been closed since 2022, so it is seen from the outside, along the quay and the coastal paths. The site is exposed to winds off the estuary.

During the French Revolution, authorities converted this military stronghold into a prison holding priests, nuns, and soldiers who resisted the new regime. This dark period shows how the tower's purpose shifted dramatically.