The history of San Casciano is closely connected to the 42 hot springs with a mean temperature of and a daily delivery of (third in Europe). According to
Livy, the thermal baths of
Balnea Clusina were founded by
Porsenna, an
Etruscan king of
Chiusi whom Roman sources date to the sixth century BC. Excavations in 2025 found objects that date the baths to the end of the 5th century BC, rather than the 3rd century BC previously believed. The finds, particularly the many anatomical votive objects in terracotta, also revealed that the baths were a major thermal healing sanctuary and also one of the foremost medical centres for the Etruscans which may have included an organised medical school. These votive finds were found in a sacred deposit, or
favissa, used after their removal from active use and covered an extraordinary range of anatomical replicas whose quantity and accuracy are unparalleled elsewhere in the ancient world. Outstanding among these is a model from about 400 BC of human internal organs with striking accuracy suggesting advanced medical knowledge and practice. It also suggests that the sanctuary was a regional centre for medical knowledge, and artisans capable of producing the models in terracotta and bronze were part of the organisation and shared expertise with healers. Other finds were closely associated with important religious ceremonies and suggest that a monumental sanctuary was near or above the thermal springs. A monumental Etruscan enclosure wall was found dating from the 3rd c. BC or earlier. The baths continued to be popular during the ensuing
Roman era,
Augustus being said to have been amongst those using the baths. Objects found from the end of the sanctuary’s life such as a bronze lightning bolt show that pagan worship ceased in the late 5th century after the
Theodosian edict and after an abandonment ritual which included ancient altars being broken and moved to form a platform between the main spring and one to the south. Also in the third to fourth centuries a Christian
Pieve of St. Mary
ad balneo existed in San Casciano. During the
Middle Ages it was initially under
Lombard rule, and later under the Visconti di Campiglia and the Abbey of San Salvatore. Troops of San Casciano took part in the
Battle of Montaperti in 1260. The last Visconti ruler was Monaldo, who also was
podestà of Florence in 1389. San Casciano was acquired by the
Republic of Siena in 1412. In Renaissance times its thermal baths attracted visitors from all over Europe, but visits began to decline in the nineteenth century, recovering only during the early twenty-first century. == Main sights ==