Now we have seen that Italy is composed of tracts of highland and tracts of lowland. The differences among the peoples ruled by Rome were due to the differences between highland and lowland, as well as to differences due to the contrast between sea and land; and the same race which had developed qualities of government on a smaller stage in Italy was able to furnish rulers for the different lands that were subdued. There were in the later Roman Empire many units whose inhabitants were naturally hostile to one another.
Again, they were united by the same methods as had been used to unite Italy. As the sea could not every where be used as a way, roads were driven over the whole of south and western Europe to such an extent as to make it a proverb that all roads lead to Rome. And the same tendency to centralized government is again to be noticed, for all the roads did lead to or from Rome : there were few cross-roads connecting various units, so that there might be as little intercommunication as possible, and the less chance of combination against the ruling power. These roads, too, naturally followed the line of least resistance ; they were constructed where there was the least expenditure of energy, so that for this reason also the distribution of high ground and low ground in the lands surrounding Italy came to have increasing importance.
A glance at a map of Europe will show that all the way from the west of the Black Sea to the Rhone there is a belt of highland over which no access can be had to the plain beyond except by rising to con siderable heights. Spain also is a tableland. In the gap between the Alps and the Pyrenees is set an isolated mountain mass with its steep edge facing southward. This does not close the entry. The Rhone valley is left to give access to the land beyond—the only easy land way from the Mediterranean northwards. Thus, though the highlands of the Alps were occupied by hostile tribes, it is little wonder that this entry, accessible from the sea, should have been easily held by the Romans, and that the whole of what is modern France should quickly have come under their rule.
Later, the Empire expanded north-eastward and east ward until, by the beginning of the Christian era, there was added to all the lands rimming the Mediterranean, which the power of the sea had given her, also those west and south of the Rhine and Danube ; while, in the east, Asia Minor and the lands west of the Euphrates owned her rule. This was the Roman Empire. Here for some three or four centuries the Pax Romana allowed of the growth of a civilization over very different and widely scattered areas, which had no natural cohesion except that which was due to their common dependence on the Roman power and administration.
Their peoples were able in peace, without spending their energies in war, to turn to useful account such advantages as their positions gave them.
The Empire had been built up by a power centralized at Rome. It owed its cohesion mainly to the military and administrative genius of its people, which was largely the result of geographical controls. Because it was the race and not an individual man who possessed this genius, the Roman Empire was not an interlude like the Macedonian Empire. It existed strong arid powerful till the fifth century of our era. In the form of the Byzantine Empire it fell only with the fall of Constantinople in 1453, and in name it lasted till the other great Alexander, Napoleon, swept away the ancient traditions in Europe. Such, again, is the strength of momentum. Because it had been it continued to be.
Like the other powers which had exercised rule over the world, the Roman Empire came to an end, but it came to an end almost as gradually as it had grown, for the great geographical controls came to make themselves felt in another way.
(a) The Mediterranean Sea is long and narrow. The Roman Empire, based on the lands rimming this sea, was thus long and narrow, about twice as long as it was broad. The desert on the south leaves between it and the sea only a narrow margin at best, so that if we consider only the land on the north of the Mediter ranean, in which was the important part of the Empire, a greater disproportion between length and breadth will be seen. There was, then, a natural tendency to divide into two parts whenever the power that held the whole together became of less effect.
(b) The eastern end of the Mediterranean was differ ent from the west. Just because it is far removed from the ocean, just because it contains the oasis lands of Egypt and Mesopotamia, and because Greece with its islands is also in this region, it is from the west in many ways easily to be recognised. The difference between east and west had been there all the time. The difference was there even before the Republic of Rome became the Roman Empire, and the difference has lasted all through history. It is no acci dent that Actium and Lepanto and Navarino should all have been fought just west of Greece where the sea forces of the Western Mediterranean meet those of the Eastern. The Roman Empire held the two parts together, but with the weakening of the bonds the parts separated.