Château de Beaumont-sur-Sarthe, Medieval castle ruins in Beaumont-sur-Sarthe, France

Château de Beaumont-sur-Sarthe is a ruined Romanesque fortress above the Sarthe in Pays de la Loire. Its original plan was an irregular rectangle about 33 m long and 22 m wide, with walls once some 30 m high and 2.5 to 3.3 m thick. Today a broken stone wall on a low red-brick base survives, pierced by one empty arched window opening, with a slender black lamp post in front.

Built between the 11th and 12th centuries for the viscounts of Le Mans and Beaumont, the castle was taken by William the Conqueror's troops in 1073 and returned to its lord in 1083. English forces burned the town and castle in 1135, and Henry V seized it in 1417. Under Louis XI the upper storey of the keep was dismantled and the walls levelled into an inner courtyard. It was listed as a monument historique on 6 January 1927.

The castle gave its name to the town that grew beside it, and the surrounding streets still follow its outline: rue du Château runs along the north-east side, rue du Mans along the west. The seigneurial residence belonged to the viscounts of Beaumont, a branch of the viscounts of Le Mans, and its stones were quarried locally, including the roussard sandstone of the buttresses.

The ruins stand just above the town centre, overlooking the Sarthe and flanked by rue du Mans to the west and rue du Château to the north-east. Only the base and the corner tower survive, so the site is read from outside; no guided tours or visitor facilities are documented.

The round tower on the north corner of the main building measured 6 metres across and was used to watch the town and its surroundings. The walls were reinforced by buttresses of local roussard sandstone about 2 metres wide and 0.80 metre deep at the south-east and north-west corners.