Château de Montoire, Medieval castle in Montoire-sur-le-Loir, France.

Château de Montoire stands ruined on a grassy spur above the left bank of the Loir, which it overlooked along with the bridge and the town. A tall round tower with a broken, jagged top rises on one side; a shattered curtain wall with an arched opening and a window void links it to a massive flat-topped rectangular keep of regular pale grey masonry. Lower crenellated walls run down the slope, and vegetation grows on the ledges.

The fortress began construction in the 11th century and underwent continuous expansion and reinforcement for over four centuries to maintain its strategic position. King Henry IV ordered its dismantling in 1593 as part of policies to reduce the power of individual families.

The name Montoire comes from the site itself, not from a Latin sanctuary; the castle was the seat of a barony held by the counts of Vendôme. Alix de Bretagne received it as her dowry and died there in 1377. In September 1549 Antoine de Bourbon and Jeanne d'Albret stayed about three months after their wedding.

The ruins stand on the edge of a hill above a dry valley on the left bank of the Loir, watching the bridge and the town below. The site belongs to the commune and is open to the public; the ground is uneven, with slopes between the towers and the curtain walls.

A dendrochronological analysis of the wooden beams shows the keep dates to around 1080, making it one of the region's oldest stone structures. This dating technique, which measures growth rings from timber, revealed the exact construction period with unusual precision.