A Swedish royal castle associated with Valdemar of Sweden's confinement and later dynastic conflict.
Nyköping Castle in Södermanland was the site of the Nyköping Banquet in December 1317, when King Birger of Sweden imprisoned his brothers Valdemar and Erik at a Christmas feast. Their subsequent confinement and death became one of the most infamous episodes of treachery in Swedish royal history.
The Nyköping Banquet destroyed Birger's political position. His brothers' deaths provoked a Swedish noble uprising that deposed him and led to the accession of Magnus Eriksson in 1319. The castle's name became synonymous with royal betrayal in Swedish historical memory.