Castelmur Castle, Medieval castle ruin in Bondo, Switzerland

Castelmur Castle is a multi-level fortification on a rock ridge above Promontogno, with three separate elements: the ruined tower Turraccia on the highest crag, the five-story square keep of the feudal castle with 2.4 m thick walls, and the valley-blocking wall Lan Müraia with its gate and 3.7 m thick flanks.

Romans built a guard station called Murus here in the third century to monitor trade traffic. During the Middle Ages, a fortress developed from this post under the authority of the Bishop of Chur, overseeing commerce through the Alps.

The ruins reveal how medieval people built their homes and defenses into steep mountain terrain to guard against threats. Visitors walking through the site can sense how the structure fit into the landscape and dominated the river passage below.

The ruins sit at 930 m above Promontogno, and the cantonal road now runs through the Promontogno tunnel beneath them. The complex has three separate levels: the Turraccia tower on the top crag, the main tower and Nossa Donna church on the middle ridge, and the Lan Müraia road barrier on the terrace above the Mera gorge. The levels were only partly connected, so allow time to move between them.

The fortress functioned as both a residence and a customs checkpoint where merchants paid tolls to trade between Italy and Switzerland. This toll system brought considerable wealth and power to its rulers through the centuries.