_De Monarchia_ is a vision of earthly well-being. It is an argument, prosaic and heavy in the English translations and very difficult in the original, I should suppose, even to an excellent Latin scholar. But the argument embodies a dream of the greatest of dreamers. The first part sets forth the necessity of empire. Only under a single world-governing monarch are possible the solidarity of mankind and the fullest possible development of the human spirit. In unity man can find peace and justice. Man is made in the image of God, and God is one; wherefore man in imitation of God must make the secular world conform to the universe and set up a unique earthly dominion. In the nature of things empire is divinely ordained and this is further proved by the fact that Christ willed to be born under the Emperor Augustus.
The second part seeks to show that the Roman empire was appointed by God to rule the world. It was established by the aid of miracles, which confirm it as especially created by the will of God. Christ died under the empire; if the empire had not been the rightful temporal authority, Christ would have been punished by the agent of an unjust power, his suffering would have been unlawful and therefore the sin of Adam would not have been duly expiated. Rome was born to command, because it did, in point of fact, conquer the world, and also because the histories of its many heroes and patriots show that the Roman citizen loved right and justice.
The third part is an argument for the separation of church and state, which are independent authorities both deriving directly from God. Many false arguments for the temporal power of the church are refuted. Though the emperor, as a man, is the first son of the church and should obey it like other Christians, yet as emperor he owes allegiance only to God, whom he represents on earth in temporal matters as the pope represents God in spiritual matters. The very nature of the church, its essential spiritual function, forbids it the possession of temporal power.
Have we here, then, nothing but a defence of an empire that has been dust these many centuries, and stale scholastic arguments for the separation of church and state, a long settled question in theoretic politics and practically settled in most countries? There is much more than that in _De Monarchia_ even for the most confident modern democrat, who may regard emperor and pope as twin tyrants and for whom the word "mediæval" has derogatory connotations. It is true that the empire under which Dante actually lived is dead as the empire of the Caesars and that the empire of Dante's dream was never realized in the workaday world. As a political pamphlet _De Monarchia_ is obsolete without even the persistent contemporaneity of some eighteenth century tracts. In a sense Dante's treatise died at birth. Bryce, who gives an excellent summary of it in his "Holy Roman Empire," shows that this plea for empire, conceived by the supreme mind of the age, was the epitaph of the existing empire. It was, indeed, a swan-song, not of the author, who was still to take us to Paradise and put his dream in lovelier form, but of empire in the Catholic Christian sense of "holy." The empire that persisted after the thirteenth century grew further and further away not only from a poet's dream but from any practical possibility of united political authority. The solidarity of mankind was not to be achieved through Rome or Christ, and Dante was not, as he thought, announcing a new era, but summing up a passing era.