On the top of the fortress rock is the church of Santa Maria de Arce that took its name from its location. Arx is Latin for fortress, high citadel. The church originally was a simple single-nave building attached to the castle and was built only for the soldiers.
Only later was it opened to the public and after the middle of the seventeenth century it was enlarged and embellished by Theodoli with aisles.
In the right aisle, there is a chapel dedicated to the Passion of Christ in which Jesus is represented in Gethsemane. For this reason, a Sepulchre is set up here in the evening of Holy Thursday.