The Commander’s House is a good example of how housing and the defensive system were connected under the same roof. The building’s side wings also functioned as fortification bastions and it was possible to access the bastion terrepleins directly from the rooms. In case of an emergency the windows of the dining room as well as of the sleeping alcove could be used as crenels from which the main entrance to the fortress, the Artillery Bay, could be defended. The building was used as the commander’s residence until 1855, when it lost its southern wing in the Crimean War.

In 1927 the Ehrensvärd Society made an initiative to establish a museum in those rooms, that had been used as commander Ehrensvärd ‘s residence. The museum was opened in 1930.