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The no-man's-land (up to 100 km across) between the Christian-controlled north and Moorish-controlled south was too insecure for arable farming and was only exploited by shepherds. When the Christians conquered the south, farmers began to settle in the grazing lands, and disputes with pastoralists were common. The Mesta can be regarded as the first, and most powerful, agricultural union in medieval Europe.
The export of merino wool enriched the members of the Mesta (the nobility and religious orders) who had acquired ranches during the process of Reconquista. Two of the most important wool markets were held in Medina del Campo and Burgos.
The kings of Castile conceded many privileges to the Mesta. The cañadas (traditional rights-of-way for sheep that perhaps date back to prehistoric times) are legally protected "forever" from being built on or blocked. The most important cañadas were called cañadas reales (or "royal cañadas"), because they were established by the king.
Some Madrid streets are still part of the cañada system, and there are groups of people who occasionally drive sheep across the modern city as a reminder of their ancient rights and cultures, although these days sheep are generally transported by rail.
The word comes from Latin animalia mixta ("mixed animals"), referring to the diverse ownership of the animals among nobles and the Church. The bringing together of animals to assign their ownership (Klein, p. 9) became a meeting of shepherds. When the council was established, it was also called mesta.
The word mustang comes from mesteño or mestengo ("a mesta [i.e. ownerless] beast").
- Julius Klein: The Mesta: A Study in Spanish Economic History 1273–1836. Harvard University Press, 1920