The Nyköping Fortress The Nyköping Fortress is first mentioned in writing in the mid-13th century. Even in the early 14th century, the fortress was a modest structure, with one central tower and a tall ring wall made of paving stones. Inside the wall were wooden houses, stables, and storage buildings. The “key” to the Nyköping Fortress The Södermanland Museum has an exhibit on King Birger’s 1317 Banquet in the King’s Tower of the Nyköping Fortress. The booth shows a model of the fortress and tells about the heinous crime committed there. It also shows a 25-cm long forged door key. The bow is ring-shaped, the stem is hollow and has a reinforcement ring just under the bow. The high bit has a large number of incisions. Is this the very door key that Eric’s Chronicle tells us Birger threw into the Nyköpingsån? The answer is no, which is clear when we look at comparable keys from elsewhere in the country. Late Gothic door locks and keys of the same type shown in the Nyköping Banquet exhibit were used in many churches in the provinces of Uppland and Västergötland, and all can be dated to the late 15th and early 16th century. Some type of lock must have been used on the brothers’ prison. The question is, was the room closed via a door in the stone wall, or a hatch in the wooden ceiling? If it was a wooden door, what types of locks were used in wooden doors in the early 14th century? The lock may have had a wooden tumbler bolt or a wooden block lock like the ones used in church doors in those days. The main exhibition in the King’s Tower contains keys for such locks. If it was a wooden trapdoor, what type of padlocks were available in those days to lock it? It might have been some kind of push-key lock with a separate shackle and ward springs. The main exhibition in the King’s Tower contains keys for such locks as well.