A modification of the theory of the divine right of kings comes in as the influence of the Papacy increases. Dante in his work _On Monarchy_ has stated the situation clearly, when he writes: “Therefore man had need of two guides for his life, as he had a twofold end in life; whereof one is the Supreme Pontiff, to lead mankind to eternal life, according to the things revealed to us; and the other is the Emperor, to guide mankind to happiness in the world, in accordance with the teaching of philosophy.” But unfortunately these two fields of activity overlapped each other, and it was not easy to say what the theoretical and practical relation of these two supreme powers to each other was. Pope Leo III had placed the crown on the head of Charlemagne in Rome in the year 800. What the Pope had given in the name of the people of the Roman world, he could take away, and at the death of an emperor, the control of the empire returned to the hands of the Pope. The great Pope, Hildebrand, in the eleventh century held firmly to this theory. As the Carlyles have pointed out, he had a search made in the papal archives and found what he believed to be convincing evidence of the feudal dependence of the different kingdoms of Europe on the Roman See. In the next century the great English scholar John of Salisbury writes in his _Policraticus_: “the sword, the symbol of worldly power, the prince receives from the hand of the Church.” Feudalism inculcated the idea that each man owed allegiance to some one above him, the vassal to his lord, the lord to the prince, the prince to the Emperor, and it was only natural to complete the system by deriving the power of the Emperor from the Pope, whose responsibility was to God. This conception of the Pope as the ultimate source of authority throughout the world with his seat in Rome continued the tradition of the unity of the Roman Empire, which, as we shall soon see, was one of the most potent influences at work throughout the Middle Ages. The history of medieval political theory and practical politics in the Middle Ages turns largely upon the conflict of these two doctrines, that the secular ruler received his authority from the people or directly from God, or that it came to him from the Pope, the vicegerent of God.