Historians and geologists believe that the Monti Pisani group is one of the most ancient mountain formations in Italy. Part of the mountains is made up of limestone rocks, a fact that has allowed the formation of cavities which in many cases have become more or less extensive caves. It should be noted that for geological science there is a rock, called Verrucana which took its name from Mount Verruca which is found in the M. Pisani (at the top of which stands the ruins of an ancient castle) and which characterizes it for its presence . Over time many populations have settled in this area and, at the dawn of Christian worship, the area was identified as an ideal place for retreat and prayer. This gave way to the construction of several churches, oratories, parish churches, allowing the development of the main town of Calci, docs the bellsima Certosa was built, which can still be visited. The hydrogeological conformation has allowed the formation of various springs ranging from San Giuliano Terme to Uliveto Terme, allowing the development of these countries made famous for their thermal baths. From one of these springs (that of Asciano) starts the splendid Medici aqueduct, begun at the behest of Cosimo I de ‘Medici and finished by his son Ferdinando at the end of the 1500s and which still arrives in the city of Pisa. Thanks to the countless paths and mule tracks it is possible to make many excursions in the Pisan Mountains: on foot, by bicycle and on horseback, which leave from the most important towns such as Vecchiano, San Giuliano Terme, Asciano, Calci and Uliveto Terme.