Ussel Castle is one of Medieval castles of Valle d'Aosta. It is located on top of the rocky ridge overlooking the village of Châtillon, in panoramic position. Castle was built by Ebalo II of Challant in 1343 and marks a change in Aosta Valley: cuboid, it is the first example of "monobloc fortress". The south side shows a series of different light windows and is adorned at the top by a band of arches and battlements. Defensive structure of the side is constituted by two circular turrets and by a machicolation above the entrance door. The north side instead has two square towers on the sides and an imposing tower with a square plan in the middle, actually with symbolic function. The interior was heavily damaged due to the abandonment and was completely rebuilt. Maybe was divided into three rooms, with the main building used as a residence of the warden and the side to service environments. Heating was provided by monumental chimneys, whose traces are still visible at different floors.