Nevertheless, isolated from the rest of the West, the Archbishop of Toledo, Primate of the Iberian peninsula Church, heir to the kingdom of the Visigoths which had fallen under Muslim domination, developed at the end of the 8^th century an interpretation of Chalcedonian  Christology which Rome judged heretic. Pope Hadrian I and Frankish theologians accused this Spanish doctrine, which has passed down to posterity under the name of  ‘Spanish Adoptionism,’ of denying the divine nature of the Saviour, in making Christ a man who was filled with the divine Spirit during his adoption by God through the effect of his baptism. Following research undertaken by John Cavadini, it is now on the contrary accepted that the Spanish Bishops’ doctrine of ‘adoptionism’ was developed in an Iberian peninsula under Arab domination, with a view to safeguarding the doctrine of the Trinity proclaimed at the First Council of Nicaea (325) through an insistence on the presence of the incarnated Son within the Trinity. Anxious to preserve belief in the Incarnation, Archbishop Elipandus of Toledo had introduced the concept of adoption to explain, in developing it, the idea of the Word being stripped of its divinity during the Incarnation. It seems that, originally, the misunderstanding between the Franks, Romans and Spanish stemmed from the discrepancy between the Latin terms adoptivus and adoptio and a Roman-Germanic juridical terminology according to which these terms dealt with a substitution of a natural relationship with an artificial but legitimate relationship, from which results a weakened from of filial status. According to this accepted meaning, talking of the adoption of the Son was tantamount to affirming an inequality in the substance of the Father and the Son, threatening the dogma of the divine Trinity. Adding to this terminological confusion a refusal to understand the Spanish attempt to elaborate the concept of the divine Person, the Frankish and Roman theologians believed that they had detected in Elipandian ‘adoptionism’ a resurgence of the serious errors condemned during the first half of the 5th century. Bolstered by the tradition of the Visigoth theological school, the powerful Archbishop Epilandus and the theologian Felix, Bishop of Urgel, did not intend to submit to the Frankish-Papal doctrinal authority. Worried by the idea that their doctrine could spread beyond the Pyrenees and shatter religious unity within the Frankish world, Charlemagne himself intervened, seconded by theologians who had gathered from the four corners of Christianity: the Papacy supported his initiative with the utmost firmness. This theological dispute moreover enabled, amongst other things, the King of the Franks to establish himself as the doughty defender of orthodoxy, as the rex praedicator. 

Charlemagne, defender of the Faith

Several theological debates related to this adoptionist problematic had as their setting the Frankish court between 767 and 799: Florence Close examines them scrupulously, stressing successively the meeting at Gentilly (767), the Councils of Regensburg (792), of Frankfurt (794) and, to a lesser extent, that of Aachen (799). The Council of Frankfurt, where the detested doctrine was rejected, has passed down into posterity as the first major council of the reign of the future Emperor: the famous Capitulary of Frankfurt bears witness to this, a text which, irrespective of the majority of the decisions dealing with multiple aspects of the governance of the Frankish kingdom, states at the beginning that ‘the very Holy Fathers [...] have decided that this [adoptionist] heresy must be radically uprooted from the Holy Church.’ Quite especially on this occasion, concludes our historian, ‘Charlemagne established himself as the uncontested head of the Frankish national church, subject to Roman authority in matters of doctrine. The Council of Frankfurt was a privileged site of thinking through the Frankish-papal alliance which the crowning of the year 800 would consecrate.’