Nassau is a geographical, historical and cultural region in today's Rhineland-Palatinate and Hesse in western Germany. Named for the town Nassau, it includes the territory of the Duchy of Nassau, a former sovereign country which existed until 1866. Occupied by Prussia and annexed into the Province of Hesse-Nassau in 1866, Nassau briefly became the name of a separate province, the Province of Nassau, in 1944. Much of the area is today part of the Nassau Nature Park. Nassau is also the name of the smaller Nassau collective municipality, the area surrounding the town of Nassau.