The Battle of Płońsk was fought on 20 October 1655 between the armies of Poland-Lithuania and Brandenburg-Prussia amid the Deluge.
By the end of October, Sweden's multi-pronged counterattack into Poland had failed. King Carl Gustaf was captured while trying to take Lublin, Fabian von Wersen was taken prisoner while attempting to capture Warsaw, and Gustav Horn was repelled during his attempt to recapture Myadzelsk Castle. Elector Frederick William led a fourth invasion force into northern Poland from Prussia, but this small army was intercepted by Jerzy Wisniewski's Polish mercenary army northwest of Warsaw on 20 October 1655. In the ensuing battle, the Brandenburgians found that their superiority in pikes could not overcome the superiority of Poland's cavalry, and the Germans were massacred to a man. Elector Frederick William was taken prisoner in another humiliating defeat at Wisniewski's hands.