The Siege of Dorsten (German: Belagerung von Dorsten) was a military conflict that lasted from 16 July 1641 to 19 September 1641 during the Thirty Years' War in Europe. The opposing sides were the Landgraviate of Hesse-Cassel and the Holy Roman Empire of the German Nation.According to a judgement by the Vienna Supreme Court (Wiener Hofgericht), Hesse-Cassel had to cede Upper Hesse, which included the University of Marburg, to Hesse-Darmstadt.