The Arab invasion of the Ebro valley in the 8th century, many Christians of the Diocese of Calahorra sought refuge in areas further north free of Arab rule. The diocese called Álava or Armentaria was established in 870 on territory split off from the Diocese of Calahorra. From then until the 11th century the names of several bishops of this see are recorded, the best known being the last, Fortún, who in 1072 went to Rome to argue before Pope Alexander II in defence of the Mozarabic Rite, which King Alfonso VI of León and Castile had decreed should be replaced by the Roman Rite.