Of all the features of that wonderful human structure, the Roman Empire, the most striking, and also the most essential, was its Mediterranean character. Although in the East it was Greek, and in the West, Latin, its Mediterranean character gave it a unity which impressed itself upon the provinces as a whole. The inland sea, in the full sense of the term Mare nostrum, was the vehicle of ideas, and religions, and merchandise. The provinces of the North — Belgium, Britain, Germany, Raetia, Noricum, Pannonia — were merely outlying ramparts against barbarism. Life was concentrated on the shores of the great lake. Without it Rome could not have been supplied with African wheat. It was more beneficent than ever now that it could be navigated in perfect security, since piracy had long disappeared. On the roads that led thither from all the provinces the traffic of these provinces converged upon the sea. As one travelled away from it civilization became more rarefied. The last great city of the North was Lyons. Treves owed its greatness only to its rank of temporary capital. All the other cities of importance — Carthage, Alexandria, Naples, Antioch — were on or near the sea ...
In the 7th century the ancient Roman Empire had actually become an Empire of the East; the Empire of Charles was an Empire of the West.
In reality, each of the two Empires ignored the other.
And in conformity with the direction followed by history, the centre of this Empire was in the North, to which the new centre of gravity of Europe had shifted. With the Frankish kingdom — but it was the Austrasian-Germanic Frankish kingdom — the Middle Ages had their beginning. After the period during which the Mediterranean unity subsisted — from the 5th to the 8th century — the rupture of that unity had displaced the axis of the world.