Bagni di Petriolo

Bagni di Petriolo is a natural thermal site in the Farma river valley, within the Ombrone basin, roughly 30 km south of Siena at the border between the municipalities of Monticiano (Siena) and Civitella Paganico (Grosseto). Hot sulphurous water flows here and mixes with the cold water of the Farma river. The official website is run as a heritage restoration and valorization project rather than as an operational spa, so it documents the history and structure of the site more than day-to-day visitor services.

Thermal water

The site states that hot sulphurous water surfaces here. Historically, visitors channelled this water into shallow pools built from stones set into the rock along the river, where the hot thermal flow blended with the cold river water. The website does not publish a measured water temperature, mineral analysis, or spring depth.

The historic complex

Bagni di Petriolo is described as a rare example of a fortified thermal establishment. The complex covers a perimeter of about one hectare, enclosed by a defensive wall averaging around six metres high with three towers and gates; the wall survives almost in its entirety apart from a section of roughly 20 metres. The upper level of the site holds a church, while the lower level, at river level, has a loggia with pools.

History

According to the site, the thermal area developed from around the 10th century, reached its greatest extent in the 13th century, and held a prominent role in the territory of Siena until the 16th century. Archaeological work has confirmed a compact medieval settlement with both private and public buildings. Until 2016, bathers still made their own shallow pools from stones at the point where thermal and river waters met.

Restoration project

A restoration and valorization initiative began in 2015, led by the association Italia Nostra together with UnipolSai as property owner, starting with pre-feasibility studies and community engagement. Design work ran from 2016 into early 2017, followed by an authorization phase in 2017 and a multi-year period of intervention. The project has drawn on expertise from the University of Siena, the Politecnico di Milano, and Sisma, a spin-off of the University of Florence. Planned works include structural repairs to the loggia, church, and walls, archaeological and environmental works, and activities such as a permanent exhibition on medieval thermal culture housed in the north tower, guided visits, publications, and 3D reconstructions.

On site

The site notes additional structures within or beside the complex, including a former inn with a restaurant that has been out of use since the 1990s and a modern, unfinished thermal building of two incomplete floors. A separate luxury resort nearby draws on the same thermal waters. The website offers guided visits (Visite Guidate) and contact information but does not publish opening hours or prices.