Monastery of San Juan de Duero, built in the Romanesque style, consists of a single nave with a wooden roof, semicircular apse, and a pointed barrel vault. From the 12th century it belonged to the Knights Hospitaller of Jerusalem, until it was abandoned in the 18th century. The 12th century church and the 13th cloister, with Gothic and Mudéjar elements, are still standing.The arcades combine the various architectural styles current in Spain at the time: late Romanesque, early Gothic, and especially, Islamic tracery. These arches are criss-crossed to achieve a beautiful visual effect. Inside the church there is a display of items from Jewish, Islamic and Christian cultures.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.