In the earlier Middle Ages the claims of the Papacy to universal supremacy had been urged and defended by ecclesiastical jurists alone; but in the thirteenth century theology also began to state them from its own point of view. Thomas Aquinas set himself to prove that submission to the Roman Pontiff was necessary for every human being. He declared that, under the law of the New Testament, the king must be subject to the priest to the extent that, if kings proved to be heretics or schismatics, the Bishop of Rome was entitled to deprive them of all kingly authority by releasing subjects from their ordinary obedience.

The fullest expression of this temporal and spiritual supremacy claimed by the Bishops of Rome is to be found in Pope Innocent IV.'s Commentary on the Decretals ( 12431254), and in the Bull, Unam Sanctam, published by Pope Boniface VIII. in 1302. But succeeding Bishops of Rome in no way abated their pretensions to universal sovereignty The same claims were made during the Exile at Avignon and in the days of the Great Schism. They were asserted by Pope Pius II. in his Bull, Execrabilis et pristinis ( 1459), and by Pope Leo X. on the very eve of the Reformation, in his Bull, Pastor Aeternus ( 1516); while Pope Alexander VI. ( Rodrigo Borgia), acting as the lord of the universe, made over the New World to Isabella of Castile and to Ferdinand of Aragon by legal deed of gift in his Bull, Inter cœtera divinae ( May 4th, 1493). The power claimed in these documents was a twofold supremacy, temporal and spiritual.

The former, stated in its widest extent, was the right to depose kings, free their subjects from their allegiance and bestow their territories on another. It could only be enforced when the Pope found a stronger potentate willing to carry out his orders, and was naturally but rarely exercised. Two instances, however, occurred not long before the Reformation. George Podiebrod, the King of Bohemia, offended the Bishop of Rome by insisting that the Roman See should keep the bargain made with his Hussite subjects at the Council of Basel. He was summoned to Rome to be tried as a heretic by Pope Pius II in 1464, and by Pope Paul II in 1465, and was declared by the latter to be deposed; his subjects were released from their allegiance, and his kingdom was offered to Matthias Corvinus, the King of Hungary, who gladly accepted the offer, and a protracted and bloody war was the consequence. Later still, in 1511, Pope Julius II. excommunicated the King of Navarre, and empowered any neighbouring king to seize his dominions--an offer readily accepted by Ferdinand of Aragon. . .