 Despite being seriously outnumbered 3 to 1, the Franco-Navarrese attacked, surprising the Spanish and gaining some initial success.But then Fadrique Enríquez, Admiral of Castile, moved his cavalry across the Sierra de Erreniega and fell upon the Franco-Navarrese rear guard.The bloody battle continued for several hours, but finally the bulk of the Franco-Navarrese was forced to surrender after suffering an estimated 5,000 casualties.