The history of the former concentration camp in Sonnenburg has not yet been sufficiently explored. However, the camp played a major role in the process of establishing and consolidating the Nazi regime. As it was subject to Prussian police authorities from April 1933 on, the transition from the constitutional state to German fascism crystallizes in the concentration camp’s history. Apart from looking at the institutionalization of the camp, its character is explored by assessing former inmates’ testimonies. A sociographic analysis of the camps’ prisoners adds to a better understanding of the societal dimension of the transition. By rediscovering the particular history of the Sonnenburg concentration camp and approaching its role for the establishment of the Nazi “dual state” (Ernst Fraenkel), this article contributes to the field of research of the so-called early concentration camps. It concludes with a discussion on the politics of memory which have recently unfolded alongside the establishment of a museum at the site of the former concentration camp.