 He was named in honour of Saint Peter, because of his father's special devotion to the Holy See, to which he had made his kingdom a vassal.Peter continued his father's close alliance with the Church and pursued his military thrust south against bordering Al-Andalus taifas with great success, allying with Rodrigo Díaz de Vivar, known as "El Cid", the ruler of Valencia, against the Almoravids.According to the medieval "Annales Compostellani" Peter was "expert in war and daring in initiative", and one modern historian has remarked that "his grasp of the possibilities inherent in the age seems to have been faultless."