Castelnau-Pégayrols (Castèlnòu de Leveson in Occitan) is a commune in the Aveyron department in southern France.

In addition to its castle and three churches it has a unique mediaeval irrigation system recognised in 1996 as of global importance.

To the east are dry limestone soils of the Causse Rouge grazed by the milking ewes that contribute to Roquefort cheese.

These soils make way in the west to the sandstones and schistes of the crystalline plateau of the Lévézou, and the humid chestnut woods.

[4] In 1258, Bernard de Lévezou (Bishop of Bézier) granted privileges to the villagers while the priory was supported by the parishes of Castelnau, St Beauzély, Éstalane and Salsac.

The Hundred Years' War ended with the Treaty of Brétigny (1360), which gave Rouergue to the English (Les Anglais).

Les Anglais was also the name used to describe roving brigands that roamed the countryside during this unstable period, Castelnau was protected by its ramparts.

[4] In the 18th century, Louis XV created the Marquisat de Pégayrolles with Castelnau as its principal town.

There exists a lodge (pond)44°07′48″N 2°55′48″E / 44.13001°N 2.93002°E / 44.13001; 2.93002 feeding a cistern in the castle,44°07′47″N 2°55′57″E / 44.12974°N 2.93242°E / 44.12974; 2.93242 from here an underground water course was built leading to three 12th century chestnut and walnut grinding watermills (recorded 1433).44°07′49″N 2°55′59″E / 44.1303°N 2.93292°E / 44.1303; 2.93292 Later four were recorded (1640-1763) but only the location of three 15th century mills is known 44°07′49″N 2°55′59″E / 44.1303°N 2.93292°E / 44.1303; 2.93292 The conduits led into a developed irrigation system for the neighbouring fields, and for a public toilet.