Excerpts from Books and Wikipedia
"On August 8, 1002, the unofficial ruler of Muslim Spain, Abu 'Amir al-Mansur ('Almanzor' to his Christian enemies), died in battle at Calatanazor against the combined armies of the Christian kingdoms of Castile and Leon. This was the last of no fewer than fifty-seven campaigns that Almanzor had led against the Christian kingdoms of northern Spain. . . . His death left a power vacuum that led eventually to the fall of the caliphate." [Furtado: 1001 Days]