As the wastes of barren land formed an almost impassable eastern boundary to the West Asian civilisations, so on the west the expanse of sea brought Egypt and to a less extent Assyria (through Phœnicia) into touch with all the peoples who dwelt on the shores of the Mediterranean. The first agents in the diffusion of trade and the arts were the Phœnicians, established at Tyre, Sidon, and Carthage. The next were the Greeks. For more than two thousand years, from B.C. 700 onwards, the Mediterranean is practically the centre of the history of the world, because it is the highway both of commerce and of war. For seven hundred years after the end of the second century B.C., that is to say, while the Roman Empire remained strong, it was also the highway of civil administration. The Saracen conquests of the seventh century cut off North Africa and Syria from Europe, checked transmarine commerce, and created afresh the old opposition of East and West in which a thousand years earlier Herodotus had found the main thread of world history. But it was not till after the discovery of America that the Mediterranean began to yield to the Atlantic its primacy as the area of sea power and sea-borne trade. [Sidenote: Influence of the Seas in History] Bordered by far less fertile and climate-favoured countries, and closed to navigation during some months of winter, the Baltic has always held a place in history far below that of the Mediterranean. Yet it has determined the relations of the North European states and peoples. So, too, the North Sea has at one time exposed Britain to attack from the Danish and Norwegian lords of the sea, and at other times protected her from powerful continental enemies. It may indeed be said that in surrounding Europe by the sea on three sides, Nature has drawn the main lines which the course of events on this smallest but most important of the continents has had to follow. [Sidenote: Magellan and American Politics]