Coming from Prato, serpentine marble or green marble was widely used in the Middle Ages because of its chromatic similarity to ancient green porphyry from the Peloponnese region. It has iridescent shades of grey, blue and very dark green, which allow for an interplay of colour. With the Romanesque style, it was mostly used in large factories, especially in Tuscany, together with Carrara marble or Alberese stone. This alternation of white and dark green, typical of the Tuscan Romanesque style, can be seen in Florence in the Baptistery of San Giovanni and in San Miniato al Monte, as well as in the cathedrals of Prato and Siena. Together with porphyry, it was used as a reference to the colours of the Byzantine translation, with red representing royalty and blue/green representing humanity.