(c) Further, the Sahara desert lies to the south of the Mediterranean, so that attack was little to be feared from that side ; westward and north-westward lay the ocean, from which no attack could come in early times, but all north-eastward and eastward was the great mass of Euro-Asia, of which Rome ruled only a rim. From this mass enemies could—and did—come. It was natural that the centre of government should be shifted eastward, nearer the frontier that required defence, in order that that defence might be more easily under taken. Because the city of Rome had been, it con tinued to be : just because it had a history, it could not at once become a provincial town, so that when Constantine set up his capital at Constantinople there were two Imperial cities within the Empire, one in the east and one in the west, and an additional impetus was given to the tendency towards disruption.
(d) Lastly, Rome had owed her very existence to the ability of her citizens to defend themselves, but just because they were far removed from any menace of attack by men outside the Empire, the later Romans gradually lost their powers both of defence and govern ment. When attacks at last did come, the barbarian hosts passed by the newer, and more virile city of Constantinople, but ancient Rome fell before them.
Thus the Roman Empire gradually divided into two parts having less and less cohesion. The eastern section continued to carry on the ancient traditions in a modified form for a thousand years, but with the fall of Rome itself the western section, far from any centralized government, became separated from the Eastern Empire and resolved itself into separate and often antagonistic units.
Then the geographical conditions controlled history in a different way from that in which they had done, because that which was to be controlled was different.
Set between forces from sea and land, but possessing no strong power within itself at a time when no strong power ruled on either land or sea, Italy was the sport of history for centuries. For a time in the hands of one power, regained for a moment by the Eastern Empire, taken and retaken in whole or in part, whenever a seaman might get a foothold or a landman settle; torn between Goth and Lombard and other Teutons from the north, and Vandal, Saracen and Byzantine in the south, it is little wonder that Italy, with the additional tendency to disruption induced by that very variety of highland and lowland which had been her strength, should have had no united history, and that consequently even till within the last sixty years the rivalries of the parts into which she was torn should have been the most noteworthy feature.
And the variety of highland and lowland of which the Empire itself was composed no less continued to control history. The units remained, and the history of the Middle Ages consists simply of a history of the arrange ments and rearrangements and re-rearrangements of these units, struggling towards the more or less perma nent state of equilibrium in modern Europe. The Roman Empire had stimulated directly or indirectly a great number of geographical units. They were brought into the world; each was civilized but in a different way, and the history of the Middle Ages is confusing simply because it is mainly the history of attempts on the part of those small and mutually jealous units to combine in stable forms. In Western Europe these units happen to be small and numerous because low ground and high ground are distributed in comparatively small areas, whose inhabitants are mutually jealous of each other.
But the importance of historical momentum must not be forgotten. Because history has to do with the minds of men, ideas have been a force in making history. Because of circumstances Rome had become an empire. The great discovery of the Romans had been that good centralized government saved energy, and the idea of empire and the methods of government remained in the minds of men as an ideal which has had an extra ordinary effect in helping to combine loosely knit units.
And this idea gained additional importance because of another fact. Because of the ancient prestige of the city of Rome, as well as because of this idea of empire, the bishop of Rome came to have a power conceded to no other. When the civil power was destroyed, the ecclesiastical authority remained, and grew all the stronger because there was no civil authority with which it clashed. Even the ecclesiastical pro vinces remained when the civil provinces with which they originally were identical had totally disappeared. Thus over the western lands of the Roman Empire rather than over the eastern Christianity spread, and the Christianity, too, of that particular type which is essentially Roman.
It was the interaction of these two allied ideals, Empire and the Church, on the natural differences due to the differences of the units, which is largely responsible for the history of the times following the fall of Rome.