The building history of the City-Theater in Grein an der Donau remained widely sketchy. Especially the structural development of the townhall in its entirety since 1563 to the present constitutes a true desideratum of research. The final result of this thesis includes the first-time presentation of all construction phases. The current question is focused on reconstruction measures for urgently needed structural repairs and redevelopment work with respect to the legal requirements. The introduction of the study reflects the present state of research and all sources used. The subsequent chapter gives an overview on the area of Strudengau and the urban development of the city Grein. The general introduction is followed by a detailed architectural analysis of the City Theatre. Finally the resulting knowledge is represented graphically. The historical and contemporary atmosphere of the City Theatre is pictured by a detailed building description and its interiors in particular. The room book captures the building in its entirety and completes the architectural and historical research. Following extensive research, the last part of the thesis shows the present reconstruction, which is still in planning stages since years, but still have not come to an end.