It was under Gregory the Great that the Papacy acquired its great supremacy over the Provincial Churches.  As the power of the Church grew after the death of Charlemagne, partly from the inclination of weak kings to lean on ecclesiastical support, the Papal claims to authority developed and began to be maintained by the penalties of excommunication and interdict.

A period of extreme laxity in the tenth century was to be brought to a close in the eleventh partly by the pressure brought to bear on the Papacy by the Saxon emperors, but still bore by the ambitious resolution of Gregory VII.  This remarkable man was determined to assert the complete supremacy of the Holy See over all secular powers.  He refused to recognise the right of secular princes to make ecclesiastical appointments within their own dominions; and he emphasised the distinction between the priesthood, as a cast having divine authority, and the laity, by enforcing with the utmost strictness the ecclesiastical law of celibacy, which completely separates the churchman from the normal interests and ambitions which actuate the layman.

In the contest between Gregory and the emperor, it seemed for the moment as if the secular power had won the victory; but, in fact, throughout the twelfth century; the claims which Gregory had put forward were becoming practically effective partly from the great influence exercised through the Crusades.  These Papal pretensions reached their climax in the great Pope Innocent III., who asserted with practical success the right to pronounce absolutely on all disputes between princes or between princes and their subjects, and to depose those who rejected his authority.  Throughout the thirteenth century Rome was once more mistress of the world.

The Church derived great influence from the institution of mendicant orders, especially those of St. Dominic and St. Francis which recovered much of the esteem forfeited by the old Monastic orders.  Another instrument of Papal influence was the power of granting dispensations both with regard to marriages and as to the keeping of oaths.  If the clergy were free for the most part from civil taxation, they were nevertheless severely mulcted by the Papacy.  The ecclesiastical jurisdiction encroached upon the secular tribunals; the classes of persons with respect to whom it claimed exclusive authority were persistently extended, in spite of the opposition of such Princes as Henry II. and Edward I.

At last, however, the Papal aggressor met his match in Philip the Fair.  When Boniface VIII. died, his successors first submitted to the French monarchy and then became its nominees; while they resided at Avignon, virtually under French control.  The restoration of the pontificate to Rome in 1375 was shortly followed by the Great Schism.  For some years there were two rival Popes, each of whom was recognised by one or the other half of Western Christendom.  This was terminated by the Council of Constance, which incidentally affirmed the supremacy of general councils over the Pope.  The following council at Basle was distinctly anti-papal; but the Papacy had the better of the contest.