Frederick Louis, Duke of Schleswig-Holstein-Sonderburg-Beck (; 6 April 1653 – 7 March 1728) was a Duke of Schleswig-Holstein-Sonderburg-Beck and field marshal of the Prussian Army. He was the son of August Philipp, Duke of Schleswig-Holstein-Sonderburg-Beck and Countess Marie Sibylle of Nassau-Saarbrücken. Life Frederick Louis was born in Haus Beck (now part of Löhne), near Ulenburg, Westphalia, Margraviate of Brandenburg. He was only the titular duke, because he did not inherit the domain of Beck. It had been inherited by Duke Frederick William I, the son of his elder brother, Duke August, in 1689. Duke Frederick William I was killed in the Battle of Francavilla in Sicily in 1719, leaving a widow, née Marie Antoine called Antoinette Josepha Isnardi di Castello, Contessa di Sanfré (1692–1762), and two minor daughters. Maria Antonia shared administration of Beck with her mother-in-law, Duchess Hedwig Louisa of Schleswig-Holstein-Sonderburg-Beck (née Countess of Lippe-Buckeburg-Schaumburg). In 1671 Frederick Louis became a cornet in the cavalry regiment von Eller in the army of Brandenburg-Prussia. In 1675 he participated in the Battle of Fehrbellin as a Rittmeister. The following year he was a colonel in the Holstein dragoons. Frederick Louis was named lieutenant general and Governor of Wesel in 1690. Three years later he was appointed commanding general of the Duchy of Prussia. On 17 January 1701 Frederick Louis received the Order of the Black Eagle from the new King Frederick I of Prussia and shortly afterward was named Statthalter of the Kingdom of Prussia and Governor of Königsberg. During the War of the Spanish Succession, he participated in the Battle of Oudenarde in 1708, the Battle of Malplaquet in 1709, and the sieges of Lille, Mons, and Tournai. Frederick Louis was promoted to field marshal in 1713. The duke also secured neutrality for Prussia during much of the Great Northern War. He died in Königsberg and was buried alongside his wife in Königsberg Cathedral. Marriage and issue On 1 January 1685 in Augustenburg, Frederick Louis married Louise Charlotte of Schleswig-Holstein-Sonderburg-Augustenburg, daughter of Ernest Günther, Duke of Schleswig-Holstein-Sonderburg-Augustenburg and Augusta of Glücksburg. They had several children: Princess Dorothea of Schleswig-Holstein-Sonderburg-Beck (24 November 1685 - 25 December 1761) Frederick William II, Duke of Schleswig-Holstein-Sonderburg-Beck (18 June 1687 - 11 November 1749) Prince Frederick Louis of Schleswig-Holstein-Sonderburg-Beck (25 August 1688 - 5 November 1688) Princess Sophie Charlotte of Schleswig-Holstein-Sonderburg-Beck (15 August 1689 - 8 October 1693) Charles Louis, Duke of Schleswig-Holstein-Sonderburg-Beck (18 September