The Castello Svevo ('Swabian' or Hohenstaufen Castle) was originally built by the Saracens on the ruins of the ancient Rocca Brutia, around the year 1000. The castle was restored by Frederick II, Holy Roman Emperor, adding the octagonal tower to the original structure, in 1239. According to tradition, his son Henry lived in this castle, as a prisoner at his father's command. Louis III of Naples and Margaret of Savoy married in the castle and they both settled there in 1432.
All signs of the ancient Saracen structure have now disappeared. In the internal cloister, the modifications made by the Bourbons in order to convert it into a prison can also be seen. The entrance-hall is covered by ogival arches with engraved brackets. A wide corridor is dominated by some fleur-de-lis from the House of Anjou coat of arms. They are engraved on the ribbed Hohenstaufen arches.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.