Gotha (German: Landkreis Gotha) is a Kreis (district) in western central Thuringia, Germany. Neighboring districts are Unstrut-Hainich-Kreis, Sömmerda, the Kreis-free city Erfurt, Ilm-Kreis, Schmalkalden-Meiningen and the Wartburgkreis. Gotha borders the Thuringian Basin in the north and east, with a low point of about 200 meters (656 feet) in the northern part of the district. Fahner Heights, a muschelkalk ridge with a height of 413 meters (1,355 feet), is located in the extreme north, between the municipalities of Tonna and Bienstädt. The land rises to about 900 meters (2,953 feet) in the Thuringian Forest, which covers the south-western area of the district. The Rennsteig hiking trail follows a ridge line through the forest. The highest point in the district is Großer Inselsberg at 916.5 m (3,007 ft), on the border with Schmalkalden-Meiningen. The southern area of the district also has 3 dams: the Ohra Dam near the village of Luisenthal, as well as the Tambach-Dietharz Dam and the Schmalwasser Dam, both in the catchment area of the Apfelstädt, near the town of Tambach-Dietharz. On the southeastern boundary of the district, between Ohrdruf and Mühlberg, is the muschelkalk Ohrdrufer Plateau which sits at an average of about 450 meters (1,436 ft). Since 1906, 49.5 km2 of this plateau has been used as military proving ground. Aside from the areas covered by the Thuringian forest and other small wooded ridges, the district is largely used for agriculture. In 1640, Gotha was partitioned from the Saxon Duchy of Saxe-Weimar to form the Duchy of Saxe-Gotha in the Holy Roman Empire. After acquiring additional territory from nearby dutchies, Saxe-Gotha was itself partitioned into seven dutchies in 1680, with the Gotha territory continuing in Saxe-Gotha-Altenburg. The duchy's ruling family line went extinct in 1825 with the death of Frederick IV, and the territory was divided again, this time into Saxe-Hildburghausen and Saxe-Coburg and Gotha.