Arnstadt is a town in Ilm-Kreis, Thuringia, Germany, on the river Gera about 20 kilometres south of Erfurt, the capital of Thuringia. Arnstadt is one of the oldest towns in Thuringia, and has a well-preserved historic centre with a partially preserved town wall. The town is nicknamed Das Tor zum Thüringer Wald because of its location on the northern edge of that forest. Arnstadt has a population of some 25,000. The city centre is on the west side of Gera. The municipality comprises four "villages": Angelhausen–Oberndorf, Dosdorf–Espenfeld, Rudisleben, and Siegelbach. The neighbouring municipalities are Wachsenburggemeinde, Kirchheim, Alkersleben, thorn Home, Wipfratal, Plaue and Gossel.