The Casa de Ganaderos de Zaragoza or Brotherhood of San Simón y San Judas (House of Livestock Breeders of Zaragoza) is an institution of medieval origin that was established to defend the privileges granted by the kings to the cattle owners of the kingdom, also bringing together corporately mayorales and herders. After seeing its powers drastically reduced since the eighteenth and nineteenth centuries, it changed its name and legal status (local board, association, union or cooperative, which is the one with which it continues to operate today; which makes it the oldest company in Spain). ^[1] The territorial breadth of its activity included ravines for the herds of sheeps transhumants from the Pyreneess valleys to the Sistema Ibérico of Teruel. As a privileged corporation of the Ancien Régime, it is similar to the Mesta Castilian, although it precedes it in time and survived it. Unlike the Crown of Castile, the Kingdom of Aragon did not create a common institution for the whole kingdom, but in each locality, independent of each other and far from royal control. ^[2][3]

After the granting to the city of Zaragoza of the extensive grazing privileges by Alfonso the Battler after the conquest of the Muslim kingdom (1118), called the privilege of the Twenty and the privilege of the Universal Pasture (granted between 1129 and 1235 to several Aragonese localities), it was necessary to create institutions to regulate it, although it was not until 18 May 1218 that King James I of Aragon appointed Domingo de Montealteto Justice of the Cattle Breeders of Zaragoza, with civil and criminal jurisdiction over such matters (civil since 1391, according to the confirmation of privileges by King John I of Aragon). In 1229 the first texts appear that name the brotherhood, headed by the Justice, who is elected from among its members (from 40 to 80 brotherhoods), in addition to other positions, such as lieutenant of Justice, councillors, ligalleros, vedaleros and scribes.^{[citation needed]}

The Zaragoza brotherhood will be the most prominent in the kingdom. The trials of the Justice were summary executions, including the death penalty, and he maintained his own gallows on the road to San Gregorio (Cascajo neighborhood). He came to have jurisdictional conflicts with the Justice of Aragon, without this institution being able to intervene in the private affairs of the Casa de Ganaderos. Conflicts with other Aragonese cities were also frequent, which provoked protests in the Cortes de Monzón of 1626 and the Cortes de Monzón of 1646.^{[citation needed]}

This wide freedom enjoyed by Zaragoza may have been the reason why in the Alterations of Aragon, in which the city of Zaragoza took up arms against King Philip II of Spain, they did not find much help from the rest of the kingdom.^{[citation needed]}

In the reign of King Philip V of Spain the judicial competences in criminal matters of the House were submitted to the Audience, and the Justice will be ratified in his appointment by the Audience.^{[citation needed]}

In 1828, King Ferdinand VII, in exchange for a substantial payment, confirmed the privileges of the House except for the jurisdictional ones, and from then on the adaptation of the institution to the contemporary economic system began. ^[4]

The archive of the House preserves documentary sources of great importance for the reconstruction of a large period of economic and social history. ^[5]

Currently, celebrating its VIII centenary in 2018, it is dedicated to the commercialization of 1st quality lamb meat, from its partners.^{[citation needed]}

There is a House of Cattlemen of Tauste, of similar origin and operation, ^[6] and another in Ejea, with a brotherhood dedicated to Santo Domingo. There were other brotherhoods in towns throughout the Ebro region, from Logroño to Tortosa, including the Brotherhoods of the Bardenas of Navarra and Aragón from 1204 and others in Aragón from 1220. With the name of mestas, there were similar institutions in Tarazona and Albarracín; and with that of ligallo in Caspe, Teruel, Daroca, Calatayud and many other towns and even villages. In the Pyrenees there were facerías, pastoral boards and assemblies of a different nature (such as the Casa del Broto), and already in the CE 18th century, the General Board of Mountain Ranchers.^{[citation needed]}