Petriolo is located in the valley of Ombrone, along the river Farma, between the villages of Monticiano and Civitella Paganico, the first is in the province of Siena while the latter is in the province of Grosseto.
Petriolo hot springs were already known by the ancient Romans, to the point that even Cicero and Marziale quoted them in some of their masterpieces. In addition, many Etruscan and Roman ruins were found both in the area of Siena and in that of Grosseto.
Petriolo thermal baths represent a well known spa in Tuscany.
However, the current toponym dates back to the XIII century.
During the Renaissance, at the beginning of the XV century, the mineral spring water was channeled in the first masonry thermal bath of the area, just in front of the river Farma, near Monticiano. The thermal complex is surrounded by walls and arcades, which were built using stones.
Petriolo thermal baths became prestigious during that historical time. As a matter of fact several representatives of the noble families of Gonzaga and Medici and the Pope Pio II himself, used to greatly appreciate the benefits of these thermal springs. In 1907 Petriolo was even mentioned by the Italian Minister of the Interior as one of the official national mineral water.