Ruotsinsalmi fortress was built by Russians in 1790-1796. It was part of the South-Eastern Finland fortification system which was planned to defence St. Petersburg. The sea fortress was located to islands in front of the city of Kotka and Kyminlinna fortress. It contained three main strongholds (Fort Katarina, Fort Elisabeth and Fort Slava) and several redoubts and artillery batteries.
Ruotsinsalmi fortress lost its original defensive value only couple of years later, when rest areas of Finland were joined to Russia after the Finnish War (1808-1809). It was disbanded in the 1830's and during the Crimean war (1855) Anglo-French fleet destroyed the empty fortress permanently.
Today individual remnants of fortresses can still be found for instance beside Catherine’s path and on the island of Tiutinen. Also Fort Elisabeth's embankments have been renovated in recent years. The island is easily accessible by regular boat services in the summer.
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.