The Sun and Moon Allegory

Pope Innocent III was determined to assert papal authority over every area possible. He made sure that kings, although they had their "local" political power, were still under the spiritual authority of the pope. Elected in January 1198, in November of that year he wrote a letter laying out something called the "Sun and Moon allegory":

Just as God, founder of the universe, has constituted two large luminaries in the firmament of Heaven, a major one to dominate the day and a minor one to dominate the night, so he has established in the firmament of the Universal Church, which is signified by the name of Heaven, two great dignities, a major one to preside—so to speak—over the days of the souls, and a minor one to preside over the nights of the bodies. They are the Pontifical authority and the royal power. Thus, as the moon receives its light from the sun and for this very reason is minor both in quantity and in quality, in its size and in its effect, so the royal power derives from the Pontifical authority the splendour of its dignity...

In the Fourth Lateran Council, called by Innocent in 1215, this philosophy was enshrined in Canon 3:

... if a temporal ruler, after having been requested and admonished by the Church, should neglect to cleanse his territory of this heretical foulness, let him be excommunicated by the metropolitan and the other bishops of the province. If he refuses to make satisfaction within a year, let the matter be made known to the supreme pontiff, that he may declare the ruler's vassals absolved from their allegiance and may offer the territory to be ruled by Catholics, who on the extermination of the heretics may possess it without hindrance and preserve it in the purity of faith; the right, however, of the chief ruler is to be respected as long as he offers no obstacle in this matter and permits freedom of action.

The Church was perfectly happy to leave the temporal authorities to do whatever they liked, so long as nothing they did contradicts or offended the laws of the Church.

Pope Boniface VIII (1294 - 1303) issued the papal bull Unam Sanctam ("One Faith") reinforcing this approach to the two estates. Dante argued against this, stating that emperor and pope each has supreme authority in their sphere, but neither is allowed to influence the other. By the end of the 14th century, belief in the pope's authority to meddle in secular matters was waning.

But in Innocent's time, he used it frequently. We'll get into specifics tomorrow.