Donjon de Houdan

Constructed around 1120-1137 by Amaury III of Montfort, the keep or donjon is the only vestige of the medieval castle of Houdan.

It is flanked by four turrets 4.8 metres in diameter each at cardinal points on the central cylinder.

The walls of the tower have an average thickness of three metres.

An access door was located 6 metres above the ground level and once gave access to the mezzanine floor.

The donjon is thought to have been one of the earliest experiments in improving flanking fire from the battlements (reduction of "dead ground"), and a transitional form between the rectangular keeps of the 11th to 12th centuries, and widespread adoption of cylindrical keeps in the 13th century.