Tour Gabriel, Medieval defense tower at Mont-Saint-Michel, France

The Tour Gabriel is a round tower of rough-cut grey and tan stone on the southwestern side of Mont-Saint-Michel. It has a diameter of 16 metres, walls two metres thick, and a corbelled parapet topped by a small conical-roofed turret, with a second similar turret attached to its upper right side. Small rectangular openings pierce the curved wall.

The tower was built in 1524, or according to some sources 1529, by military engineer Gabriel du Puy, after whom it is named. A tower at this spot had already been planned in 1479. It defended the western cliffs of Mont-Saint-Michel and controlled the Couesnon. In 1637 a windmill was added on top, and in the late 19th century a lighthouse or semaphore served shipping on the Couesnon until its removal in 1902.

The tower's name honours Gabriel du Puy, the military engineer credited with building it in 1524, though some sources give 1529. A windmill was set up on top in 1637; its base survives as the central watch turret crowned by the conical roof. In the late 19th century a lighthouse or semaphore stood here to guide shipping on the Couesnon, and it was dismantled in 1902 once the river was no longer navigable.

The tower stands on the southwestern side of Mont-Saint-Michel, reached by the rampart walkways from the village entrance. The ground around its base is jagged rock, and the paved path beside it is narrow, so sturdy shoes help. The three floors are linked by stairs built around the central hexagonal pillar.

The hexagonal pillar inside is hollow and pierced at several points; it is thought to have served as a speaking tube for communication between floors. The 15 gunports were fitted with closable covers, as on warships of the period, and allowed all-around, cross and flanking fire.