Boniface VIII issues Unam Sanctam
Since the middle of the eleventh century popes had been asserting their power over secular rulers. They claimed that the spiritual authority ordained by God held precedence over mere earthly power. They had deposed kings and emperors and named substitute rulers; they had precipitated civil wars; claimed dominion over entire kingdoms and excommunicated princes right, left and centre. By 1300 they had gutted the power of their chief rival, the Holy Roman Emperor and begun to quarrel with the new centralized monarchies of western Europe.
Benedetto Caetani, elected Pope Boniface VIII in dubious fashion in 1294, had twice forbidden the kings of England and France from taxing the Church in their countries. The King of France Philip IV “the Fair” responded by cutting off money from the French church to the papacy. Boniface replied by hinting that he might exercise his right of deposing Philip who immediately began a campaign of vilification of the pope including circulating forged documents.
This led Boniface on November 17, 1302 to issue the proclamation Unam Sanctam, which asserted the doctrine of papal monarchy in the most uncompromising terms ever. He asserted (1) there is but one true Church, outside of which there is no salvation; (2) that head is Christ and His representative, the pope who is above, and can direct, all kings; (3) whoever resists the highest power ordained by God resists Himself; and (5) it is necessary for salvation that all humans should be subject to the Roman Pontiff.
Philip the Fair now summoned a kingdom-wide assembly, and before it he accused Boniface of every imaginable crime from murder to black magic to sodomy to keeping a demon as a pet. A small French military force crossed into Italy in 1303 and took Boniface prisoner at his palace at Anagni with the intention of bringing him to France for trial. The French plan failed—local townspeople freed Boniface a couple of days later—but the proud old pope died shortly thereafter, outraged that anyone had dared to lay hands on his sacred person.
This marks the beginning of the waning of medieval papal power. In 1305 the cardinals elected the Frenchman Clement V who submitted to the French king on the question of clerical taxation and publicly burned Unam Sanctam, conceding that Philip the Fair, in accusing Pope Boniface, had shown “praiseworthy zeal.” A few years after his election, Clement moved the papacy from Rome to Avignon in southern France, the start of the period of papal humiliation known as “The Babylonian Captivity”.