Western monasticism had been greatly extended and organised by Benedict of Nursia and his rule—­comprised in silence, humility, and obedience.  Monasticism became possessed of the papal chair in the person of Gregory the Great.  Of noble descent and of great wealth, which he devoted to religious uses as soon as he became master of it, he had also the characteristics which were held to denote the highest holiness.  In austerity, devotion, and imaginative superstition, he, whose known virtue and capacity caused him to be forced into the papal chair, remained a monk to the end of his days.

But he became at once an exceedingly vigorous man of affairs.  He reorganised the Roman liturgy; he converted the Lombards and Saxons.  And he proved himself virtual sovereign of Rome.  His administration was admirable.  He exercised his disciplinary authority without fear or favour.  And his rule marks the epoch at which all that we regard as specially characteristic of mediaeval Christianity—­its ethics, its asceticism, its sacerdotalism, and its superstitions—­had reached its lasting shape.

Gregory the Great had not long passed away when there arose in the East that new religion which was to shake the world, and to bring East and West once more into a prolonged conflict.  Mohammedanism, born in Arabia, hurled itself first against Asia, then swept North Africa.  By the end of the seventh century it was threatening the Byzantine Empire on one side of Europe, and the Gothic dominion in Spain on the other.  On the other hand, in the same period, Latin Christianity had decisively taken possession of England, driving back that Celtic or Irish Christianity which had been beforehand with it in making entry to the North.  Similarly, it was the Irish missionaries who began the conversion of the outer Teutonic barbarians; but the work was carried out by the Saxon Winfrid (Boniface) of the Latin Church.

The popes, however, during this century between Gregory I. and Gregory II. again sank into a position of subordination to the imperial power.  Under the second Gregory, the papacy reasserted itself in resistance to the Emperor Leo the Isaurian, the “Iconoclast,” the “Image-breaker,” who strove to impose on Christendom his own zeal against images.  To Leo, images meant image-worship.  To his opponents, images were useful symbols.  Rome defied the emperor’s attempt to claim spiritual dictatorship.  East and West were rent in twain at the moment when Islam was assaulting both West and East.  Leo rolled back the advancing torrent before Constantinople, as Charles Martel rolled it back almost simultaneously in the great battle of Tours; but the Empire and the West, Byzantium and Rome, never presented a united front to the Moslem.

The Iconoclastic controversy threw Italy against its will into the hands of the image-worshipping Lombards; and hate of Lombard ascendancy turned the eyes of Gregory’s successors to the Franks, to Charles Martel; to Pepin, who obtained from Pope Stephen sanction for his seizure of the Frankish crown, and in return repressed the Lombards; and finally to Charles the Great, otherwise Charlemagne, who on the last Christmas Day of the eighth century was crowned (Western) emperor and successor of the Caesars.