count of Nassau-Dietz and Stadtholder of Friesland, Groningen and Drenthe. Ernst Casimir was primarily known as an outstanding military leader during the Eighty Years War. He served under Maurice of Nassau, Prince of Orange in the siege of the cities of Steenwijk and Oldenzaal, and Frederick Henry, Prince of Orange during the Siege of Groenlo (1627) and the Siege of 's-Hertogenbosch. As Stadholder of Groningen he founded the Nieuweschans fortress in 1628.
