St Aubin's Fort was developed on a rocky islet off the coast at the western end of St Aubin's Bay. It was finished in the 1540s. At that time St Aubin was the primary port on Jersey and the fort controlled the entrance. In the 17th century the Civil War the Parliamentarians turned it into a stronger fortress, by building a bulwark on it, and when the Royalists regained possession they replaced this with granite ramparts and added a storey to the tower. In the 18th century, and again in the 19th, the fort was rebuilt twice, but in peaceful Victorian times it was let as a summer residence. In the Second World War the Germans strengthened the fort with turret guns and concrete casemates.
A causeway extends from the road in front of the Royal Channel Islands Yacht Club to the fort, and one can walk out at low tide. However, the fort itself is closed to the public. Jersey's Sea Scouts use the fort as a headquarters, storing their sails and other equipment in a German bunker built into the fort. They have also converted a room in the tower into a classroom.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.