One of the most important churches of Mystras is the Cathedral of Agios Demetrios, built in 1280- 1292. It is the oldest church in the city.
This church has a mixed architectural style: on the one hand it has a three-aisled basilica with a narthex and a bell tower, built in the 13th century on the ground floor, and on the other hand, the upper floor is a cross-in-square church, added in the first half of the 15th century. Its interior is decorated with wall paintings in many different styles. This is where the last Byzantine emperor, Constantinos Paleologos, was crowned in 1449.
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.