During the 13th century Prussian Crusade, the current Gvardeysk area was conquered by the Teutonic Knights. To protect Samland from the Nadrovians and Scalovians, the crusaders built a wooden fort between the Deime and Pregel rivers from 1283–90. This was replaced by Tapiau Castle, a stone Ordensburg, in 1351. Vytautas, forthcoming grand duke of Lithuania was baptised here in 1383 after he breached of Krėvė prison. Since 1450 town and castle was named Tapiau. After Teutonic state was downed by Poland and Lithuania, Teutons moved order archives to Tapiau castle and kept it during 1469-1722. Later Tapiau castle was abbandoned. Soviets built a jail on the mound, it remains active.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.