He was the 11th child of
John VI, Count of Nassau-Dillenburg, and
Countess Elisabeth of Leuchtenberg. After the death of his father, his counties
Nassau-Dillenburg,
Nassau-Siegen,
Nassau-Dietz, and
Vianden were divided among his five living sons. Ernest Casimir followed him as
Count of Nassau-Dietz. In 1631, he inherited the small county of Spiegelberg near
Lauenstein. Ernest 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 and the
Siege of 's-Hertogenbosch. As
Stadtholder of Groningen, he founded the
Nieuweschans fortress in 1628. Although he owned little in Friesland, he was popular there, and people granted his heir the right to rule after his death. He was killed by a bullet at the siege of Roermond while he was inspecting the trenches in June 1632. The hat he was wearing when he was shot and killed is now in the
Rijksmuseum in
Amsterdam. His son,
Henry Casimir I, succeeded him as count of Nassau-Dietz and as
Stadtholder of Friesland,
Groningen and
Drenthe. == Family ==