Arnstadt is a town in Ilm-Kreis, Thuringia, Germany, situated on the Gera River. It is one of the oldest towns in Thuringia and is nicknamed Das Tor zum Thüringer Wald, The Gate to the Thuringian Forest.
Modern Arnstadt has a population of approximately 25,000. It is a manufacturing center, with glassworks and foundaries, as well as glove-manufacturing and wood-finishing businesses. Manganese is one of the ores mined in the vicinity.
The composer Johann Sebastian Bach, whose family lived for generations in the vicinity of Arnstadt, began his musical career in the city. Most Bach scholars believe his well-known "Toccata and Fugue in D Minor" was written here between 1703 and 1709.