The Butter Box (Smörasken in Swedish) is a caponier built in the 16th century. It is a semi-circular fortification protruding from the wall and connected to a full-length tower. The caponier had three floors, a low cellar and two artillery decks on top. Here, the military doctrines of two separate ages met: firearms and crossbows. Crossbowmen could guard the high, inaccessible crest of the wall. The introduction of firearms risked making the wall more vulnerable, and so the caponiers were introduced. The caponiers such as this one enabled flank firing along the wall with cannons.
