The origins of Hrušov castle are not known, but it was probably built after the invasion of Tatars around 1253. From 1321 to 1344 it belonged to the family Levické and then became a royal property. In 1347 King Louis I of Hungary gave it to the governor Hrušov. The castle was destroyed by the Imperial army in 1708 and is in decay since then. However, its surviving walls induce a romantic atmosphere and provide a nice panoramic view.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.