At the top of a hill overlooking the "Conca de Tremp" (Tremp Basin), there is a group of monuments that could be represent a large part of medieval life: the Castell de Mur and, at barely one hundred metres in size, the Col·legiata de Santa Maria de Mur. These two buildings are symbols of spiritual and military domination of a border territory that had just been conquered by Muslims. They were lands under the jurisdiction of one of the prominent names of the medieval Pallars: Arnau Mir de Tost.

The architectural structure of the castle is simple but very unique and consists of a walled perimeter and boat-shaped ground floor, which has a unique gateway with southern access. The area is 31 metres long and the one-metre-thick wall has a height that varies between 14 and 18 metres. It forms a slightly irregular triangle, because of the rock on which it is constructed, with rounded corners. It is an exemplary piece of the civil military architecture of the eleventh century, with exceptionally well-conserved perimeter walls.

All the work is constructed with a small and regular bond, characteristic of the First Romanesque, and conserved within the enclosure, there lies the circular master tower; about 16 metres high, divided into four floors and bearing loophole windows.