Mollusc communities at 88 mainly medieval sites of ruined castles, churches, and chapels in Lower Franconia were studied. Depending on the conditions prevailing on the different sites, the data were recorded for the mesostructures regarded as suitable habitats for molluscs (walls, open copings, moats) and separately for the castle mounts. In addition each ruin is described in a short historical treatise, together with a view to its actual remains and the human influence to the local mollusc community. The distribution and current stock in Lower Franconia are described for some selected species whose presence at the ruin sites appears to be important for faunistic, ecological or historical reasons.