Treaty of Marienburg
The Treaty of Marienburg dated 23 June 1656 and was in Marienburg between Elector Frederick William of Brandenburg- Prussia and King Charles X Gustav of Sweden closed contract.
The reason for the conclusion of this contract, was the deteriorating political and military situation of the Swedish King Charles X during the Second Northern War, which forced him to win Brandenburg as an alliance partner.
The treaty confirmed the conclusions in the Treaty of Königsberg of January 17, 1656 Brandenburg- Swedish alliance, also King Charles X Gustav gave the area occupied by the Swedish army from 1655 Polish region of Greater Poland with the provinces of Posen and Kalisch to the Elector Friedrich Wilhelm.
Sweden guaranteed Friedrich Wilhelm assistance against any attack on its possessions. The Elector of Brandenburg also agreed to provide 4,000 men auxiliary troops for the Swedish - Polish war.