[102] I do not mean to say that the system of ideas which it is endeavoured to set forth in the following pages was complete in this particular form, either in the days of Charles or in those of Otto, or in those of Frederick Barbarossa. It seems to have been constantly growing and decaying from the fourth century to the sixteenth, the relative prominence of its cardinal doctrines varying from age to age. But, just as the painter who sees the ever-shifting lights and shades play over the face of a wide landscape faster than his brush can place them on the canvas, in despair at representing their exact position at any single moment, contents himself with painting the effects that are broadest and most permanent, and at giving rather the impression which the scene makes on him than every detail of the scene itself, so here, the best and indeed the only practicable course seems to be that of setting forth in its most self-consistent form the body of ideas and beliefs on which the Empire rested, although this form may not be exactly that which they can be asserted to have worn in any one century, and although the illustrations adduced may have to be taken sometimes from earlier, sometimes from later writers. As the doctrine of the Empire was in its essence the same during the whole Middle Age, such a general description as is attempted here may, I venture to hope, be found substantially true for the tenth as well as for the fourteenth century. [103] Empires like the Persian did nothing to assimilate the subject races, who retained their own laws and customs, sometimes their own princes, and were bound only to serve in the armies and fill the treasury of the Great King. [104] Od. iii. 72:-- ἢ μαψίδιως ἀλάλησθε, οἷά τε ληϊστῆρες, ὑπεὶρ ἅλα, τοίτ' ἀλόωνται ψυχὰς παρθέμενοι, κακὸν =ἀλλοδαποῖσι= φέροντες; Cf. Od. ix. 39: and the Hymn to the Pythian Apollo, I. 274. So in II. v. 214, ἀλλότριος φώς. [105] Plato, in the beginning of the Laws, represents it as natural between all states: πολεμὸς φύσει ὑπάρχει πρὸς ἁπάσας τὰς πόλεις. [106] See especially Acts xvii. 26; Gal. iii. 28; Eph. ii. 11, sqq.; iv. 3-6; Col. iii. 11. [107] This is drawn out by Laurent, _Histoire du Droit des Gens_; and Ægidi, _Der Fürstenrath nach dem Luneviller Frieden_. [108] 'Romanos enim vocitant homines nostræ religionis.'--Gregory of Tours, quoted by Ægidi, from A. F. Pott, _Essay on the Words 'Römisch,' 'Romanisch,' 'Roman,' 'Romantisch.'_ So in the Middle Ages, Ῥωμαῖοι is used to mean Christians, as opposed to Ἕλληνες, heathens. Cf. Ducange, 'Romani olim dicti qui alias Christiani vel etiam Catholici.'