Sancho Garcés III (c. 992–996 – 18 October 1035), also known as Sancho the Great (Spanish: Sancho el Mayor, Basque: Antso Gartzez Nagusia), was the King of Pamplona from 1004 until his death in 1035. He also ruled the County of Aragon and by marriage the counties of Castile, Álava and Monzón. He later added the counties of Sobrarbe (1015), Ribagorza (1018) and Cea (1030), and would intervene in the Kingdom of León, taking its eponymous capital city in 1034.
He was the eldest son of García Sánchez II and his wife Jimena Fernández.
The year of Sancho's birth is not known, but it is no earlier than 992 and no later than 996. His parents were García Sánchez II the Tremulous and Jimena Fernández, daughter of Fernando Bermúdez, count of Cea on the Leonese frontier. García and Jimena are first recorded as married in 992, but there is no record of their son Sancho until 996. The first record of the future king is a diploma of his father's granting the village of Terrero to the monastery of San Millán de la Cogolla. The king describes Sancho merely as "my son" (filius meus). The same diploma also shows the future duke of Gascony, Sancho VI, at the court of Pamplona.
Sancho was raised in the monastery of Leyre. His father last appears in 1000, while Sancho is first found as king in 1004, inheriting the kingdom of Pamplona (later known as Navarre). This gap has led to speculation as to whether there was an interregnum, while one document shows Sancho Ramírez of Viguera reigning in Pamplona in 1002, perhaps ruling as had Jimeno Garcés during the youth of García Sánchez I three generations earlier. On his succession, Sancho initially ruled under a council of regency led by the bishops, his mother Jimena, and grandmother Urraca Fernández.
Sancho aspired to unify the Christian principalities in the face of the fragmentation of Muslim Spain into the taifa kingdoms following the Battle of Calatañazor. In about 1010 he married Muniadona of Castile, daughter of Sancho García of Castile, and in 1015 he began a policy of expansion. He displaced Muslim control in the depopulated former county of Sobrarbe. In Ribagorza, another opportunity arose. The 1010 partition of the county left it divided between William Isarn, illegitimate son of count Isarn, and Raymond III of Pallars Jussà and his wife, Mayor García of Castile, who was both niece of Isarn and aunt of Sancho's wife. In 1018, William Isarn tried to solidify his control over the Arán valley, but was killed, and Sancho jumped on the opportunity to take his portion, presumably based on some loose claim derived from his wife. Raymond and Mayor annulled their marriage, creating a further division finally resolved in 1025 when Mayor retired to a Castilian convent and Sancho received the submission of Raymond as vassal. He also forced Berengar Raymond I of Barcelona to become his vassal, though he was already a vassal of the French king. Berengar met Sancho in Zaragoza and in Navarre many times to confer on a mutual policy against the counts of Toulouse.
In 1016, Sancho fixed the border between Navarre and Castile, part of the good relationship he established by marrying Muniadona, daughter of Sancho García of Castile. In 1017, he became the protector of Castile for the young García Sánchez. However, relations between the three Christian entities of León, Castile, and Navarre soured after the assassination of Count García in 1027. He had been betrothed to Sancha, daughter of Alfonso V, who was set thus to gain from Castile lands between the rivers Cea and Pisuerga (as the price for approving the marital pact). As García arrived in León for his wedding, he was killed by the sons of a noble he had expelled from his lands.
Sancho III had opposed the wedding and the expected expansion of Leonese power to Castile, and used García's death to reverse this. Using the pretext of the protectorship he had exercised over Castile, he immediately occupied the county and named as successor his own younger son Ferdinand, who was nephew of the deceased count, bringing it fully within his sphere of influence.
Sancho established relations with the Duchy of Gascony, probably of a suzerain–vassal nature, him being the suzerain. In consequence of his relationship with the monastery of Cluny, he improved the road from Gascony to León. This road would begin to bring increased traffic down to Iberia as pilgrims flocked to Santiago de Compostela. Because of this, Sancho ranks as one of the first great patrons of the Saint James Way.
Sancho VI of Gascony was a relative of King Sancho and spent a portion of his life at the royal court in Pamplona. He also partook alongside Sancho the Great in the Reconquista. In 1010, the two Sanchos appeared together with Robert II of France and William V of Aquitaine, neither of whom was the Gascon duke's suzerain, at Saint-Jean d'Angély. After Sancho VI's death in 1032, Sancho the Great extended his authority definitively into Gascony, where he began to mention his authority as extending as far as the Garonne in the documents issued by his chancery.
In southern Gascony, Sancho created a series of viscounties: Labourd (between 1021 and 1023), Bayonne (1025), and Baztán (also 1025).
After the succession of Bermudo III to León, Sancho negotiated the marriage of his son Ferdinand to Sancha, the former fiancée of García Sánchez and Bermudo's sister, and along with it a dowry that included disputed Leonese lands. Sancho was soon engaged in a full-scale war with León, and combined Castilian and Navarrese armies quickly overran much of Bermudo's kingdom, occupying Astorga. By March 1033, he was king from Zamora to the borders of Barcelona.
In 1034, even the city of León, the imperiale culmen (imperial capital, as Sancho saw it), fell, and there Sancho had himself crowned again. This was the height of Sancho's rule which now extended from the borders of Galicia in the west to the county of Barcelona in the east. In 1035, he refounded the diocese of Palencia, which had been laid waste by the Moors. He gave the see and its several abbacies to Bernard, of French or Navarrese origin, to whom he also gave the secular lordship (as a feudum), which included many castles in the region. However, he died on 18 October 1035 and was buried in the monastery of San Salvador de Oña, an enclave in Burgos, under the inscription Sancius, gratia Dei, Hispaniarum rex.
Before his death in 1035, Sancho divided his possessions among his sons. Of the three surviving sons by Muniadona, the eldest, García, had already appeared as regulus in Navarre, inheriting the kingdom including the Basque country as well as exercising suzerainty over the kingdom's lands given to his brothers. Gonzalo had been placed in control of the counties of Sobrarbe and Ribagorza, which he would hold as regulus. Ferdinand had been given Castile on the death of count García Sánchez in 1029, holding it first under his father and later of Vermudo III of León, before killing that king to take León and the royal title. Ramiro, the eldest but illegitimate son of Sancho by mistress Sancha of Aybar, was given property in the former county of Aragón with the provision that he should ask for no more lands of his brother García, under whom he first acted as baiulus but from whom he later achieved de facto independence. Documents report two further sons, a second Ramiro and Bernard, but scholarship is divided on whether they were legitimate sons who died in youth, or if their appearance instead results from either scribal error or forgery. Sancho left two daughters, Mayor and Jimena, the former perhaps the wife of Pons, Count of Toulouse, the latter the wife of Vermudo III.
Taking residence in Nájera instead of the traditional capital of Pamplona, as his realm grew larger, he considered himself a European monarch, establishing relations on the other side of the Pyrenees.
He introduced French feudal theories and ecclesiastic and intellectual currents into Iberia. Through his close ties with the count of Barcelona and the duke of Gascony and his friendship with the monastic reformer Abbot Oliva, Sancho established relations with several of the leading figures north of the Pyrenees, most notably Robert II of France, William V of Aquitaine, William II and Alduin II of Angoulême, and Odo II of Blois and Champagne. It was through this circle that the Cluniac reforms first probably influenced his thinking. In 1024 a Navarrese monk, Paterno of San Juan de la Peña from Cluny, returned to Navarre and was made abbot of San Juan de la Peña, where he instituted the Cluniac custom and founded thus the first Cluniac house in Iberia west of Catalonia, under the patronage of Sancho. The Mozarabic rite continued to be practiced at San Juan, and the view that Sancho spread the Cluniac usage to other houses in his kingdom has been discredited by Justo Pérez de Urbel. Sancho sowed the seeds of the Cluniac reform and of the adoption of the Roman rite, but he did not widely enact them.