Lake Montepulciano and the nearby Lake Chiusi, which are connected by the Canale del Passo alla Querce, are all that remains of the marsh which once occupied most of the Val di Chiana until the times of the de’ Medici family and which has undergone constant reclamation works in recent centuries. Partly because of the size of the area involved, the work proved to be incredibly complex, involving engineers, mathematicians, plumbers, cartographers, agronomists and architects in the various phases: from Leonardo da Vinci to Vittorio Fossombroni from Arezzo (1754 – 1844), a farsighted technician who worked on this huge and very demanding project for over fifty years.

The Canale Maestro della Chiana represents a work of historical hydraulic engineering that still plays an important role in the area today. In ancient times, the River Clanis flowed south into the Tiber, via the River Paglia. In around the 11th century, the valley began to become marshy due to the slow rise of the land in the Chiusi area, as a result of tectonic movements and the deposit of materials generated by erosion. This made it impossible for the River Clanis to continue flowing to the Tiber, causing it to flood the valley for five centuries. The initial intervention of the de’ Medici family and, later, of the Habsburg-Lorraines, who became Grand Dukes of Tuscany, began the process of transformation of the valley.

With the reclamation work and the construction of the Canale Maestro, through floodplains, canals, bridges, tunnels, locks and sluices, the watercourse changed direction and it still continues northwards, flowing into the River Arno. The result, after centuries of marshland, is in front of our eyes: one of the most fertile valleys in Italy; 185 square kilometres of land, 80 of which have been reclaimed from the water and protected by 630 km of embankments.