The marble frieze patterns of the cathedral of Siena: Geometric structure, multi-stable perception and types of repetition

The marble pavement of the Cathedral in the Tuscan city of Siena in Italy has been described as one of the marvels of the world. Over the centuries much has been written about its biblical and political characters, the stories depicted in its figurative mosaics, the artists responsible for creating the mosaics, the types of marble used and the history of their construction. The many frieze patterns framing the figurative mosaics are noteworthy examples of geometric design, and yet, they have been conspicuously overlooked in the literature concerning this pavement. Here, the geometric frieze patterns found on the pavement, walls and ceiling of the Siena Cathedral are analysed in terms of their underlying geometric structure, the optical effects, such as multi-stable perception, that they engender in the viewer and a typology of patterns of repetition.