Witch tower, Medieval fortification tower in Sion, Switzerland

The Tour des Sorciers in Sion is a round tower of three storeys topped by a crenellated parapet, originally flat-roofed. Its base and lower level were filled with rubble against mining, and the upper floors are pierced with arrow slits. The side facing the town was left open, and a stair turret and annex were added in 1753.

The round tower was probably built in the 14th century at the north-west corner of Sion's last town wall, which predates it. In the second half of the 16th century a roof was added and prisons were installed; in 1753 the cells were refitted and a stair turret and annex with new corridors were added, along with a torture chamber. It ceased to serve as a prison after the revolution, survived the demolition of the ramparts and became a historic monument in 1883.

The name "Witch Tower" appeared at the start of the 19th century and became widespread in its second half. The tower was never used for witch trials; it served as a prison until after the French Revolution. Today it regularly hosts exhibitions.

The tower stands in the north-west corner of Sion's old town, where the last city wall once ran; the Tour du Guet is the only other surviving tower. The moat dug about 7.5 m in front of it, 3.5 m deep and 12 m wide, was farmed in quiet periods and could be flooded in times of trouble. Exhibitions are held inside regularly, so check locally before planning a visit.

The tower's name only appeared in the early 19th century and spread in the second half of that century; the building itself was probably raised in the 14th century and was first called the round tower. It survived the demolition of Sion's last city wall, and since 1883 it has been listed as a historical monument.