At this epoch appears another title, of which more must be said. To the accustomed 'Roman Empire' Frederick Barbarossa adds the epithet of 'Holy.' Of its earlier origin, under Conrad II (the Salic), which some have supposed[236], there is no documentary trace, though there is also no proof to the contrary[237]. So far as is known it occurs first in the famous Privilege of Austria, granted by Frederick in the fourth year of his reign, the second of his empire, 'terram Austriæ quæ clypeus et cor sacri imperii esse dinoscitur[238]:' then afterwards, in other manifestos of his reign; for example, in a letter to Isaac Angelus of Byzantium[239], and in the summons to the princes to help him against Milan: 'Quia ... urbis et orbis gubernacula tenemus ... sacro imperio et divæ reipublicæ consulere debemus[240];' where the second phrase is a synonym explanatory of the first. Used occasionally by Henry VI and Frederick II, it is more frequent under their successors, William, Richard, Rudolf, till after Charles IV's time it becomes habitual, for the last few centuries indispensable. Regarding the origin of so singular a title many theories have been advanced. Some declared it a perpetuation of the court style of Rome and Byzantium, which attached sanctity to the person of the monarch: thus David Blondel, contending for the honour of France, calls it a mere epithet of the Emperor, applied by confusion to his government[241]. Others saw in it a religious meaning, referring to Daniel's prophecy, or to the fact that the Empire was contemporary with Christianity, or to Christ's birth under it[242]. Strong churchmen derived it from the dependence of the imperial crown on the Pope. There were not wanting persons to maintain that it meant nothing more than great or splendid. We need not, however, be in any great doubt as to its true meaning and purport. The ascription of sacredness to the person, the palace, the letters, and so forth, of the sovereign, so common in the later ages of Rome, had been partly retained in the German court. Liudprand calls Otto 'imperator sanctissimus[243].' Still this sanctity, which the Greeks above all others lavished on their princes, is something personal, is nothing more than the divinity that always hedges a king. Far more intimate and peculiar was the relation of the revived Roman Empire to the church and religion. As has been said already, it was neither more nor less than the visible Church, seen on its secular side, the Christian society organized as a state under a form divinely appointed, and therefore the name 'Holy Roman Empire' was the needful and rightful counterpart to that of 'Holy Catholic Church.' Such had long been the belief, and so the title might have had its origin as far back as the tenth or ninth century, might even have emanated from Charles himself. Alcuin in one of his letters uses the phrase 'imperium Christianum.' But there was a further reason for its introduction at this particular epoch.