Nothing, however, was so calculated to stir up the rancor of the Greeks against the Latins as the Pope’s coronation of Charlemagne as Emperor of territory that was regarded as an integral part of the Byzantine Empire. For the Greeks then held the theory, which was subsequently so elaborated by Dante in his _De Monarchia_, that the cause of Cæsar was the cause of Christ and that the perfection of the Church presupposed the integrity of the Empire and harmonious relations between Pope and Emperor. When, therefore, the Roman Patriarch set up a rival Augustus in the person of Charlemagne and divided the Roman Empire, which, under Justinian, extended from the Euphrates to the Pillars of Hercules, he was in the estimation of the Byzantines guilty of high treason. Claiming that they alone had the direct line of imperial continuity they would never recognize Charlemagne as anything more than “a barbarian King of a barbarian people.”[337] To what extent the establishment of the Empire in the West contributed to existing friction and to the fatal rupture between New Rome and Old Rome, which occurred seventy years later, is a matter of speculation, but it can scarcely be doubted that its effect on the exacerbated temper of the Greeks was far greater than is usually imagined. Although, during the first five centuries of its existence, the See of Constantinople had several times been out of communion with Rome, the “Great Schism,” as it is called, was not inaugurated until Photius, with the connivance of the Byzantine Emperor, iniquitously usurped the Patriarchate of New Rome. After the death of this intruder in 891 peace was again restored between the Eastern and Western Churches. But the schism that had been engendered by the misunderstandings and animosities, jealousies and ambitions, of centuries was healed only temporarily. For but a little more than a century and a half had elapsed after the mortal remains of Photius--who has been called “the Luther of the Orthodox Church”--had been moldering in an unknown grave when the Byzantine Church was again, in 1050, thrown into schism by the overweening ambition of Michael Cerularius, whom the Emperor Constantine IX had, in violation of the most sacred laws of the Church, foisted into the See of Constantinople as its Patriarch.