Castelberg Castle, Castle ruin in Ilanz/Glion, Switzerland.

Castelberg is a castle ruin in Switzerland's Graubunden region, built around a substantial residential tower enclosed by a surrounding ring wall. The central tower measures approximately 9 by 9 meters, features thick stone walls, and rises four stories high.

Castelberg was built in the first half of the 13th century, though no written records of its construction survive. It was the home castle of the Castelberg family, unfree knights serving the Bishop of Chur, first mentioned in 1289 with Wilhelm. The family's estates around the castle appear in a 1391 document. The castle was abandoned in the early 14th century as the family expanded into Schams, Domleschg and Vorarlberg, and by the late Middle Ages it was already a ruin.

The castle gave its name to the von Castelberg family, first recorded in 1289 with Wilhelm. Around 1500 the lineage split into two branches: one stayed in Ilanz, the other settled in Disentis after the Reformation. The Disentis branch produced three abbots of that abbey and ten men who served thirty times as Landrichter of the Grey League.

From the PostAuto stop at the junction of the road to Luven, a footpath leads to the ruin in about 10 minutes. The tower itself cannot be entered. The ring wall is overgrown and partly collapsed, and the north wall is missing, so watch your step on the slope.

Excavations in 1968 uncovered red plaster residue on the walls, pointing to a major fire that swept through before the castle was abandoned. This evidence reveals the ruin experienced a sudden, violent end rather than a gradual decline.