Waléran, the first Count of Arlon, built a fortified chateau at the top of the town during the 11th century. Along with the town ramparts, this was completely destroyed in 1558 when Arlon was pillaged by the troops of the Duc de Guise. When the Capuchin monks arrivedin Arlon in 1621, they built their abbey on the ruins of the castle.
In 1681 a Vauban-type fortified wall was built transforming the abbey into a citadel. After being the victim of alightning strike in 1719, it was decided to dedicate the church to Saint Donat. The old religious foundation of the Capuchins was finally abandoned in 1796 - Only the church survived and was then restored and renovated during the 20th century.References:
Kristiansten Fortress was built to protect the city against attack from the east. Construction was finished in 1685. General Johan Caspar von Cicignon, who was chief inspector of kuks fortifications, was responsible for the new town plan of Trondheim after the great fire of 18 April 1681. He also made the plans for the construction of Kristiansten Fortress.
The fortress was built during the period from 1682 to 1684 and strengthened to a complete defence fortification in 1691 by building an advanced post Kristiandsands bastion in the east and in 1695 with the now vanished Møllenberg skanse by the river Nidelven. These fortifications were encircled by a continuous palisade and thereby connected to the fortified city. In 1750 the fortress was modernized with new bastions and casemates to protect against mortar artillery.