The Banu Qasi leader Mūsā ibn Mūsā, following the death of Íñigo Arista, has pursued a policy of closer allegiance with Muhammad I of Córdoba, leaving García to look to Christian Asturias for an ally.

In 859, Mūsā ibn Mūsā allows a contingent of Vikings to pass through his lands and attack Navarre, resulting in the capture of García, who is forced to pay at least seventy thousand gold dinars in ransom.

Later the same year, Mūsā ibn Mūsā attacks the Pamplonese city of Albelda.

García and his new friend Ordoño I of Asturias together deal Mūsā a crushing blow, killing, it is said, ten thousand of his magnates in the Battle of Monte Laturce.