The fortified towers, or keeps, of Kurrholmen and Godnatt were built in 1857-63. This type of stronghold had existed in Europe since the Middle Ages and these two were the last such fortifications to be built in Sweden. Obsolete before they were completed, the towers had been overtaken by developments in artillery such as the rifled barrel, and could not withstand the onslaught of modern shellfire.

Gun batteries had been placed on Pantarholmen, Björkholmen and Stumholmen almost from the very beginning. In particular, it was necessary to protect the town and naval base from the Russian galley fleet. These oared warships were able to operate easily in the waters of the archipelago and harried the coasts of Sweden in the beginning of the eighteenth century. The defences on Mjölnarholmen from 1727 were built in part to prevent hostile forces from coming over the ice to attack the town. A few years later a magazine was erected on Ljungskär.

Several bastions were built to defend the town, dockyard and harbour, although the number actually constructed was considerably less than planned. The Kungshall Bastion is from the middle of the 1680’s, and the Aurora Bastion was completed in 1704. In the beginning of the 1750’s quarters were built inside the bastion to house those merchant seamen who were contracted for temporary service in the Navy. In 1756 these quarters were taken over by the Naval Hospital, which remained there until the end of the nineteenth century when a new hospital was built on Vallgatan. The park in the Aurora Bastion was laid down when the hospital was moved to Vallgatan.