Balcun At, Castle ruin in Müstair, Grisons, Switzerland

Balcun At is a ruined spur castle on a steep ridge in the municipality of Müstair, 230 metres above the valley floor at the southern edge of Val Brüna. The core structure measures 41 metres diagonally. On the highest point, remains of a nearly square tower about 10 metres wide with walls 1.2 to 1.5 metres thick survive, along with a 20-metre section of wall on the west side and a rock-cut neck ditch.

The castle's construction date is unknown; its layered masonry and traces of opus spicatum point to the 12th or 13th century. Its size above the bishop's monastery of Müstair suggests it was built with episcopal consent, possibly by ministerials linked to the Hohenbalken family. Charcoal traces at the tower and west wall indicate a fire; collapse on unstable ground is also possible, and one report attributes its destruction to Rudolf von Planta during the Bündner Wirren. In September 2000 and 2001, the Burgenverein Graubünden, the municipality of Müstair and the Berufswahlschule Bülach uncovered and secured endangered wall remains.

The name first appears in 1427 as "Janutt Carl de Balkun ault", Germanised as Hohenbalken; it derives from a high balcony or gallery. Several women of the Hohenbalken family entered Müstair monastery, three became abbesses, and Ursula V (r. 1640–1666) had the Hohenbalken room in the Plantaturm furnished, now shown in the monastery museum.

The ruin is easily reached by a marked walking trail from the village of Müstair. Visitors should bring water and wear sturdy shoes, as the ground around the ruins is uneven and there are no facilities on the mountain.

The name Hohenbalken first appears in 1427 in the form "Janutt Carl de Balkun ault". It derives from a high balcony or gallery, from Latin altus for high; the name was later Germanised and the balcony became a beam. Three women of the Hohenbalken family were elected abbesses of Müstair, including Ursula V (r. 1640–1666), who had the Hohenbalken room in the Planta tower furnished; it can be visited in the monastery museum.