Cuéllar Castle is conserved in good condition, and it has been built in different architectural styles between the 13th and 18th century. Much of the castle in the Gothic and Renaissance styles. The military building was extended and transformed in the 16th century, turning it into the palace of the Duke of Alburquerque. Among its historical owners, stands out Álvaro de Luna and Beltrán de la Cueva, as well as the successive Dukes of Alburquerque.
The Dukes of Alburquerque lived in this castle for centuries until they moved to Madrid to be close to the court. Thereafter their use of the castle was as leisure and holidays palace, abandoning the building slowly. At the late 19th century the castle was almost completely abandoned, and was victim of robberies. In 1938 was a political prison was settled within the castle, and after was established also a sanatorium for prisoners affected by tuberculosis. It was used as prison till 1966.
In 1972, the Department of Fine Arts carried out an intensive restoration, and made it the home of a Vocational Education school, which continues to this day.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.