The medieval roots of modern scientific thought. A Fibonacci abacus on the facade of the church of San Nicola in Pisa

A marble intarsia on the main entrance of the church of San Nicola in Pisa provides the opportunity to appreciate the level of cultural excellence achieved by the Maritime Republic at the height of its power during the twelfth and thirteenth centuries. The intarsia reveals the direct influence of the great Pisan mathematician Leonardo Fibonacci due to the presence of circles whose radii represent the first nine elements of the Fibonacci's sequence and which were arranged to depict some properties of the sequence. Moreover, the tiles can be used as an abacus to draw sequences of regular polygons inscribed in a circle of given radius. This construction is a novelty that has resurfaced after eight hundred years of neglect and its implications, in themselves, are worthy of special examination. The presence of so many symbolic references makes the intarsia an icon of medieval philosophical thought and reveals aspects that pave the way to modern scientific thought.