The Wilhelmsburg Castle in the city of Schmalkalden was a secondary residence of the Landgraves of Hesse. It is one of the most important Renaissance buildings in central Germany, which has experience

William IV of Hesse-Kassel, also called William the Wise, was the first Landgrave of the Landgraviate of Hesse-Kassel. He was the founder of the oldest line, which survives to this day.