Around 1900, monument preservation in Germany began to change significantly. Central demands of the reformers included the recognition of monuments as historical sources - expressed, among other things, in the famous motto by Georg Dehio, 'Conserve, do not restore' - and the renunciation of imitative architecture in independent new buildings and extensions. This work examines the fundamental positions, the debates surrounding particularly significant projects, and, above all, the most important preservation measures of the time itself.