The Mesta was a powerful association of sheep holders in the medievalKingdom of Castile.

The sheep were transhumant, migrating from the pastures of Extremadura and Andalusia to Castile and back according to the season.

The no-mans-land (up to 100km across) between Christian Spain and Moorish Spain was too insecure for arable farming and was only exploited by shepherds. When the land was reconquered by the Spanish, farmers began to settle and disputes with pastoralists were common. The Mesta can be regarded as the first, and most powerful, agricultural union in medieval Europe.

The exportation of merino wool enriched the Mesta members (nobility and church orders) who had acquired ranches during the process ofReconquista.

The kings of Castile conceded many privileges to the Mesta. Even today, herds of sheep may be transported by rail, but the perhaps prehistoric cañadas are legally protected "forever" from occupation and barring.

Some Madrid streets are still part of the cañada system, and there are groups that organize sheep transportation across the modern city as a reminder of ancient rights and cultures.