The castle of the Arlon’s first count, Waléran, was built on the hilltop in the 11th century. It was destroyed in 1558 along with the city walls by the troops of Henry I, Duke of Guise. When the Capuchin monks came to Arlon in 1621, they built their monastery on the castle ruins. In 1861, a fortified, “Vauban” style wall was erected, turning the monastery into a citadel. The church, which was struck by lightning in 1719, was dedicated to Saint Donat. The old Capuchin monastery was definitely destroyed in 1796. Only the church remained and was later redeveloped in the 20th century.