King James I of Aragon
receives from Vidal de Canyelles, Bishop of Huesca
, the first compilation of the Furs d'Aragó
(the "Fueros of Aragon"), 1247
Fuero dates back to the feudal era: the lord could concede or acknowledge a fuero to certain groups or communities, most notably the Roman Catholic Church, the military, and certain regions that fell under the same monarchy as Castile or, later, Spain, but were not fully integrated into those countries.
The relations among fueros, other bodies of law (including the role of precedent), and sovereignty is a contentious one that influences government and law in the present day. The king of León, Alfonso V, decreed the Fuero de León (1017), considered the earliest laws governing territorial and local life, as it applied to the entire kingdom, with certain provisions for the city of León. The various Basque provinces also generally regarded their fueros also known as jauntxos as tantamount to a municipal constitution. This view was accepted by some others, including President of the United States John Adams. He cited the Biscayan fueros as a precedent for the United States Constitution. (Adams, A defense…, 1786) This view regards fueros as granting or acknowledging rights. In the contrasting view, fueros were privileges granted by a monarch. In the letter Adams also commented on the substantial independence of the hereditary Basque Jauntxo families as the origin for their privileges.
In practice, distinct fueros for specific classes, estates, towns, or regions usually arose out of feudal power politics. Some historians believe monarchs were forced to concede some traditions in exchange for the general acknowledgment of his or her authority, that monarchs granted fueros to reward loyal subjection, or (especially in the case of towns or regions) the monarch simply acknowledged distinct legal traditions.
In medieval Castilian law, the king could assign privileges to certain groups. The classic example of such a privileged group was the Roman Catholic Church: the clergy did not pay taxes to the state, enjoyed the income via tithes of local landholding, and were not subject to the civil courts. Church-operated ecclesiastical courts tried churchmen for criminal offenses. Another example was the powerful Mesta organization, composed of wealthy sheepherders, who were granted vast grazing rights in Andalusia after that land was "reconquered" by Spanish Christians from the Muslims (see Reconquista). Lyle N. McAlister writes in Spain and Portugal in the New World that the Mesta's fuero helped impede the economic development of southern Spain. This resulted in a lack of opportunity, and Spaniards emigrated to the New World to escape these constraints.