Monterotondo Marittimo is a medieval castle that appears for the first time in written documentation in 1128, but the area had already been the subject of interest by the major players in Tuscan history since the 8th century thanks to its mineral resources. Its territory has always belonged to the diocese of Volterra, but it was the bishop of Lucca who owned large tracts of land in a landscape that must have been very similar to the present one, with a predominance of woodland.
However, there are also numerous indications of state ownership that certainly date back to Roman times and are related to the mineral resources. Excavations carried out by the University of Siena in the Rocca degli Alberti in Monterotondo have made it possible to date the beginning of the formation of this centre to the 9th century. This data is now available in the form of illustrative panels within a visitor route. In the same period in which Monterotondo developed, other castles, subjected to archaeological investigation by the University of Siena, saw the emergence of settlements, later surrounded by walls, between the 11th and 12th centuries. These include Cugnano, which is relatively well preserved and has a circular shape. Of particular note are the production facilities linked to the copper and silver metallurgical activities. It was precisely the mineral wealth that brought the strong powers of the time into conflict, among whom the Counts Aldobrandeschi and later the Pannocchieschi obviously stood out.
The municipal territory of Monterotondo Marittimo is also rich in places to visit from a naturalistic standpoint. For trekking enthusiasts, a mandatory stop is the Geosito delle Biancane, part of the Parco delle Colline Metallifere – Tuscan Mining UNESCO Global Geopark, so named because of the white colour of the rocks on the surface. The route is always open and free of charge, starting from Via dei Lagoni Boraciferi, winding through fumaroles and boraciferous lakes and leading to the geothermal power plants. Unlike elsewhere, the geothermal fluids in this area do not encounter any obstacles and therefore reach the surface. The MUBIA is a geo-museum where visitors can find detailed explanations on the subject of geothermal energy and, more generally, on the geological history of this area, which is rich in evidence of great value. Visiting routes include some religious places such as the church of Santa Croce, the oratory of the Madonna di Montenero and the sanctuary of the Madonna di Frassine.