The so-called "Early Concentration Camps", also known as "unofficial concentration camps," were established as of March 1933 for the imprisonment of political opponents, among them communists or social democrats. Lacking a standard or uniform underlying system, most of these camps were provisionally set up in locations already used to similar ends and ceased to exist after a few months. The camps were under the control of the SA or Gestapo. They were supplanted by the new-established and systematized ulterior concentration camps. Dachau, the first concentration camp, became the model for the concentration camp system.