The town of Monteroni d’Arbia is home to a beautiful fortified watermill, dating to the first half of the 14th century. The impressive building appears among the properties of the nearby Cuna grange, as testified by several documents of the 16th century, including one dated 1590 that bears the estimate of the rent due for a sum of 8 liras. From this and another previous document (1552), we know that the Mill worked with two millstones, though it possessed four, probably because of a decrease in flow of the waters that supplied the millrace. The fascinating hydraulic system with its round-arch conduits permitted the water to arrive inside the mill to produce hydraulic energy, and then return outside with its chemical-physical properties unchanged. Recent studies have shown that in its period of greatest activity, the Mill could produce up to half a ton of flour per day.