 Alfonso VI, from his exile in Toledo, obtained the support of the Leonese nobility and his sister Urraca, who remained strong in the city of Zamora, a lordship that Ferdinand I had granted her previously.When Urraca refused to exchange Zamora for other cities that Sancho had offered her in an effort to control the fortress of Zamora, "key to the future expansion south of the Duero", Sancho besieged the city.However, during the siege, Sancho II was murdered.