Château de Beaumont-sur-Oise

Beaumont-sur-Oise Castle was a medieval spur castle built in the 11th century on a rocky outcrop above the Oise, serving until the 12th century as the seat of the Counts of Beaumont. Strategically it controlled the river crossing on the road from Paris to the north. After decline in the late Middle Ages, only a section of curtain wall and the remains of a keep survived; since 1999 they have been protected as a Monument historique. Today the ruin is a free, open-air spot above town with views into the Oise valley.