A little south of the town Valiano, along the Principal Canal of the Chiana, is found the ‘Large Canal’ of Valiano, an important engineering work for the control and regulation of the flow of the upper Valdichiana. The name originates from the word ‘calla’, ‘sluice-gate opening, in a water course’. Until the beginning of the XVIII century the work of reclamation in the Val di Chiana had been a source of worry for the neighbouring Papal Governor, who feared a devastating effect by flooding on the Tiber, so ordered the construction of embankments near to the border, in an attempt to reduce the possible flow of the water into the Tiber. In 1781, to resolve the controversy between the Grand-duchy and the Papal State, at Città della Pieve and Sarteano, a meeting was promised between the representatives of Pope Clement XI and the Grand-duke Cosimo III. This resulted in the signing of an agreement (Concordia) that, principally for economic problems, was only put into effect in 1723 with the construction of the Regulator (or Large Canal) of Valiano, planned by the engineer Giovanni Franchi.
The best description of the Callone- Large Canal is that made by Giovan Battista Del Corto in his "History of the Val di Chiana" (1898): "The regulator or large canal of Valiano, constructed by a embankment of earth joined by the two bordering hills, and by a bricked slope on the Canal provided with sluice-gates and guarded by keepers, to help restrain the upper waters, that of Montepulciano and Chiusi and of the adjacent countryside, when considered superfluous or dangerous for the lower valley, and to introduce it, by opening the sluice-gate, when there is a shortage of water for navigation or watering of animals. As well the large canal could be the support office for goods which could pass via boats into the Lakes of Montepulciano and Chiusi and vice versa going down there on the lower canal, onto which was added a lateral regulator to maintain in summer the principal canal sufficiently deep for navigation or for the use of the mills, fed by the water of the hills of the aforesaid lakes.


On the part of the Papal State, in 1741 was built, in the Roman Chinetta, a similar regulator or large canal.
In 1944 the Large Canal was mined by the Germans retreating, and fortunately, only partially destroyed.