Crete senesi are literally ‘Siennese clays’ and the distinctive grey colouration of the soil gives the landscape an appearance often described as lunar. This characteristic clay, known as mattaione, represents the sediments of the Pliocene sea which covered the area between 2.5 and 4.5 million years ago. In the nearby is also the semi-arid area known as Accona Desert.
Perhaps the most notable edifice of this area is the monastery of Monte Oliveto Maggiore.