The Crete Senesi is a very special landscape south-east of Siena, whose clayey soil has origins in an ancient sea basin with sediments of sand and mud. Itcomprises the communes of Asciano, Buonconvento, Monteroni d'Arbia, Rapolano Terme and San Giovanni d'Asso.
The area was submerged by the sea until about one million years ago. After the withdrawal of water, the irregular deposits of clay and sand layers revealed many fossils of mussels of various kinds. Phenomena of erosion are the characteristic formations called "calanche" and "biancane", small dome-shaped hills, on which, after exposure to the sun, sodium sulfate has come to the surface, giving them a characteristic light colour. With the time, these natural events have made the landscape of the Crete one of the most unique and fascinating in Tusca ny. The main characteristic of Crete is thus a prominent and leading nature of the environment, made of very unusual colours such as the grey of clay and the yellow of sulfate. Since the Middle Ages, the whole area was known by the name of “Desert of Accona”.