Château de Bocsozel, Medieval castle ruins in Mottier, France.

Château de Bocsozel are castle ruins on a hilltop near Mottier with two surviving towers standing above the valley. The round tower was built from river pebbles and features a vaulted ground level.

Two charters from the Cathedral of Grenoble cartularies name the site: castrum Bocizelo on 25 January 1000 and, with some reservations, castrum Bocissello on 2 April 1003. These are the earliest mentions of the Humbertiens, Count Humbert and his brothers. The round tower is dated to the 13th–14th centuries.

The name Bocsozel appears as castrum Bocizelo in a charter of 25 January 1000 and as Bozosello around 1140. The round tower is built of river pebbles, a local material, and keeps a vault at its first level. The second tower has an unusual plan combining a quadrilateral and a pentagon.

Visitors should wear sturdy shoes as the paths to the ruins are steep and require some effort to climb. The trail begins at Mottier church and follows a forest path through woodland to the hilltop.

Behind the ruins, to the west, lies the old castle mound, reached by a simple wooden ladder over a fence. The round tower is the best-preserved part of the castle and was linked to the second tower by a curtain wall.