Born atZamora, Sancho was the eldest son ofFerdinand the Great andSancha of León. He was married toAlberta, known by name only from her appearance as Sancho's wife in contemporary charters. ChroniclerWilliam of Poitiers related that competition for the hand of a daughter ofWilliam I, King of England led to strife between two sons of Ferdinand I, and some historians have thus speculated that Sancho's wife, with her non-Iberian name, may have been the daughter in question. However, two later Norman chroniclers report that it wasAlfonso VI's betrothed, and not Sancho's wife Alberta, who was William's daughter.
After Ferdinand the Great defeated and killed his wife's brotherin battle, he was crowned King ofLeón and Castile and called himselfImperator totius Hispaniae ("Emperor of all of Spain"). When the kingdom was divided following Ferdinand's death in 1065, Sancho succeeded his father as King of Castile, while Sancho's younger brotherAlfonso become King of León and his youngest brotherGarcía became king of the reestablished Kingdom of Galicia (partitioned from León). Each of the brothers was also assigned a sphere of influence among theTaifa states, with Sancho designated to receive theparias (tributary payments) from theTaifa of Zaragoza. Ferdinand also granted some holdings to his two daughters, givingUrraca control of the city ofZamora andElvira the city ofToro, bothenclaved within Alfonso's Kingdom of León.
In 1068, Sancho defeated his cousinsSancho IV of Navarre andSancho of Aragon in theWar of the Three Sanchos. This expanded his Kingdom of Castile with the reconquered land ofBureba,Alta Rioja, andÁlava, which his father had given to Sancho IV's father,García, for his support in defeatingBermudo III of León. The same year, Alfonso invaded theTaifa of Badajoz, aclient state of his brother Garcia's Kingdom of Galicia. Sancho, concerned that Alfonso had intentions on conquering his brothers, defeated Alfonso at theBattle of Llantada, reinstating the status quo. Sancho would develop his own appetite for his youngest brother's kingdom: teaming up with Alfonso in 1071, Sancho marched across León to conquer García's northern lands at the time that Alfonso was in the southern part of the Galician realm issuing charters. García fled to exile in theTaifa of Seville, while his older brothers partitioned the Kingdom of Galicia between them.
Sancho soon turned on Alfonso. In 1072, with the aid of hisalférezEl Cid, at theBattle of Golpejera, he defeated Alfonso, who fled into exile in theTaifa of Toledo. Sancho was crowned King of León on 12 January 1072, holding all three crowns that Ferdinand had distributed to his sons only six years earlier. Toro, the city of Sancho's sister Elvira, fell easily in 1072. Sancho was stalled in a siege of his sister Urraca's better-defended city, Zamora.
A Zamoran noble, Vellido Adolfo (also known as Bellido Dolfos), entered Sancho's camp pretending to be a deserter and assassinated him.[1][2] Vellido was chased back to Zamora by El Cid, but escaped into the town through a gateway since calledPortillo del Traidor ("Gateway of the Traitor"). Sancho was succeeded in his kingdoms by the brother he had previously deposed, Alfonso. García, induced to return from exile, was deceived by Alfonso and imprisoned for life, leaving Alfonso in uncontested control of the reunited territories of their father, later taking on their father's title "Emperor of all Spain". Sancho was buried inSan Salvador de Oña.
^The New Cambridge Medieval History: Volume 4, c.1024–c.1198, Part 2 (The New Cambridge Medieval History, Series Number 4) by David Luscombe pg. 166-167
^“The entire subject of the murder of Sancho Il is most unclear in the literature of the times. It is difficult not to suspect the infanta Urraca of having arranged it, but there is no real evidence that she did. Even the name of the assassin, "Velliti Ariulfi," is completely unknown to the documents.” The Contest of Christian and Muslim Spain 1031 - 1157 by Bernard F. Reilly pg. 42
Bernard F. Reilly,The Contest of Christian and Muslim Spain, 1031-1157, Blackwell Publishing Ltd., 1995.
Jaime de Salazar y Acha, 1992–1993. "Contribución al estudio del reinado de Alfonso VI de Castilla: algunas aclaraciones sobre su política matrimonial",Anales de la Real Academia Matritense de Heráldica y Genealogía, vol. 2, pp. 299–336.