Dachau was one of the first concentration camps built by Nazi Germany and the longest-running one, opening on 22 March 1933. The camp was initially intended to intern Hitler's political opponents, which consisted of communists, social democrats, and other dissidents. It is located on the grounds of an abandoned munitions factory northeast of the medieval town of Dachau, about 16 km (10 mi) northwest of Munich in the state of Bavaria, in southern Germany. After its opening by Heinrich Himmler, its purpose was enlarged to include forced labor, and eventually, the imprisonment of Jews, Romani, German and Austrian criminals, and, finally, foreign nationals from countries that Germany occupied or invaded. The Dachau camp system grew to include nearly 100 sub-camps, which were mostly work camps or Arbeitskommandos, and were located throughout southern Germany and Austria. The main camp was liberated by U.S. forces on 29 April 1945.