A truce between Castile and Córdoba had existed since the succession of Sancho García of Castile, but in 999 it had been broken when the count refused to pay the annual tribute and came to the aid of his Christian neighbor, García Sánchez II of Pamplona, when Almanzor attacked him.

On June 21, 1000, an army leaves Córdoba under Almanzor for a punitive expedition against Castile.

The subsequent campaign is the most well-recorded of Almanzor's many wars after his Compostela campaign of 997.

The primary historian is Ibn al-Khatib, who derived his Arabic account partially from Ibn Hayyan, himself relying on the eyewitness testimony of his father, Jalaf ibn Husayn ibn Hayyan, one of the combatants on the Muslim side and a secretary to Almanzor.

Ibn al-Khatib records that the campaign was the most intense and difficult Almanzor ever waged, that preparations took an especially long time, and that all the rulers of Christian Spain were allied against him, with troops from all the Christian realms assembled together.