The Romans built a guard station and village named "Murus" according to the 3rd century Itinerarium Antonini.

In 960 Emperor Otto I granted the castle and right to collect tolls to the Bishop of Chur to help secure this important alpine trade route.

In 988 Emperor Otto III confirmed his grandfather's grant to the Bishop and specifically mentioned both the castle and the nearby Nossa Donna Church.

To discourage the Planta family from trying to completely annex the lucrative castle and tolls, in 1410 the Bishop mortgaged it to Jacob Perutt von Castelmur for 150 Gulden.

In addition to the castle, he repaired and rededicated the nearby church of S. Maria (Nossa Donna).

[5] The original fortification was a wall or letzi that straddled the valley between the Maira river and the castle hill.

This tower allowed a noble family to take up residence and changed Castelmur from a toll collecting station into a regional administrative center.