Symmetry analysis of the floor ornaments of the San Marco cathedral in Venice

The marble floor ornaments of San Marco Cathedral in Venice are analysed according to their symmetries and motifs. We find that all the possible crystallographic plane symmetry groups are represented with the exception of threefold symmetric p3, p3m1, p31m, and sixfold symmetric p6mm. The occurrence of the fourfold-symmetry group p4mm prevails with a rich collection of motifs. The wealth of this symmetry may have resulted from the aim to cover the surface with crosses in order to keep the evil forces away from the sacred place.