Château de Beaumont-sur-Oise

The Château de Beaumont-sur-Oise is a ruined medieval castle in the commune of Beaumont-sur-Oise in the Val-d'Oise département of France.

It has been listed since 1992 as a monument historique by the French Ministry of Culture.

History
This ancient castle is one of the most important in the valley of the Oise. It has a rectangular Romanesque keep with buttresses 25m high and 5m wide. It was probably built by the count Mathieu (1090-1151) to replace a preceding timber structure of the castrum type which had existed from the 3rd century on this rocky outcrop. It was destroyed and rebuilt several times between the 10th and 17th centuries and was no more than a ruin by the 19th.

The town was developed and structured around the castle, with construction in the 10th century of the castle's collegiate church and of a parish church.

In 1226, Louis XI became Count of Beaumont and lived in the castle.

The Hundred Years' War and the Wars of Religion were the reason for the upper part of the walls and the keep. Indeed the English occupied the town for forty years and the castle itself between 1420 and 1435, when the artillery of Henri IV caused major damage to the towers of the fortress.

Today
The walls were cleared and restored in 1997.

Archaeological excavations carried out from 1984 have revealed the existence of an 11th-century monastery.