The Battle of Fehrbellin was fought on June 18, 1675 (Julian calendar date, June 28th, Gregorian), between Swedish and Brandenburg-Prussian troops. The Swedes, under Count Waldemar von Wrangel (stepbrother of Riksamiral Carl Gustaf Wrangel), had invaded and occupied parts of Brandenburg from their possessions in Pomerania, but were repelled by the forces of Frederick William, the Great Elector, under his Feldmarschall Georg von Derfflinger near the town of Fehrbellin. Along with the Battle of Warsaw (1656), Fehrbellin was crucial in establishing the prestige of Frederick William and Brandenburg-Prussia's army. Prelude Prior to the battle the Swedes and Brandenburg had been allies in various wars against the Kingdom of Poland. However, when Elector Frederick William during the Franco-Dutch War had joined an allied expedition with Emperor Leopold I to Alsace against the forces of King Louis XIV of France, the French persuaded Sweden, which had been increasingly isolated on the continent, to attack Brandenburg while her army was away. When Frederick William, encamping at Erstein, heard of the attack and occupation of a large part of his principality in December 1674, he immediately drew his army out of the coalition but had to take winter quarters at Marktbreit in Franconia. Leaving on 26 May 1675, he marched to Magdeburg in only two weeks. This feat was considered one of the great marches in military history. He did it by abandoning his supply wagons and leaving large parts of the infantry behind, having his army buy supplies from the locals, but forbidding pillaging. The Swedes did not expect him to arrive that early. Once he returned to Brandenburg, Frederick William realized that the Swedish forces, occupying the swampy Havelland region between Havelberg and the town of Brandenburg, were dispersed and ordered Derrflinger to take the central town of Rathenow in order to split them roughly down the middle. The elector bribed a local official loyal to him to hold a large and elaborate banquet for the Swedish officers of the fortress in order to get them drunk before the assault began in the night of June 14. This ruse, combined with the speed of the Elector's advance made the Swedes unaware of his arrival. Field Marshal Derfflinger then personally led an attack on Rathenow with 7,000 cavalry and 1,000 musketeers, his approach slowed but hidden by heavy rain. Derfflinger impersonated a Swedish officer and convinced the guards to open the gates of