In the Moslem Caliphate men were now busy in following up the old lines of trade, the immemorial traditions of the East, or as in southern Africa, extending the sphere of commercial activity and so of civilisation; men of science were commenting on the ancient texts of Greeks and Latins, or adapting them to enlarged knowledge.

But in Christendom, in the atrophy both of mental and physical activity, broken for short periods and in certain lands by the revivals of Charles the Great, of the Isaurian Emperors, of Otto I., of Alfred and his House, the practical energy of Heathen enemies,—for the Northmen were not seriously touched by Christianity till about the end of the first millennium,—was the first sign of lasting resurrection. After the material came the spiritual revival; the whole life of the Middle Ages awoke on the conversion of the Northern nations and of Hungary; but in the abundant and brilliant energy of the eleventh, the twelfth, the thirteenth centuries, we must recognise the offspring of the irrepressible Norsemen as well as of the Irish and Frank and English missionaries, who in the Dark Ages of Christendom were working out the empire of Innocent III.

In exploration, especially, it was true that theory followed achievement. Flavio Gioja, of Amalphi, did not apply the magnet to navigation—did not "give sailors the use of the magnet"—till navigation itself had begun to venture into the unknown Atlantic. The history of geographical advance in the earlier Middle Ages is thus rather a chronicle of adventure than of science.

But the Norse discoveries are not only the first, they are the leading achievements of Western travel and enterprise in the true Unknown, between the time of Constantine and the Crusades. The central fact of European expansion in the Dark Ages (from the seventh to the eleventh century) is the advance of the Vikings to the Arctic Continent and to America about the year 1000. All that precedes this on the same line is doubtful and unimportant. For, of the other voyages to the West in the sixth, the eighth, the tenth centuries, which, on Columbus' success, turned into prior claims to the finding of the New World, there is not one that deserves notice.

St. Brandon in 565, the Seven Spanish Bishops in 734, the Basques in 990 may or may not have sighted their islands of "Antillia," of "Atlantis," of the "Seven Cities." They cannot be verified or valued, any more than the journeys of the Enchanted Horse or the Third Calendar. We only know for certain a few unimportant, half-accidental facts, such as the visits of Irish hermits to Iceland and the Färoes during the eighth century, and the traces of their cells and chapels—in bells and ruins and crosses—found by the Northmen in the ninth.

It was in 787 that the Vikings first landed in England; by the opening of the next century they were threatening the whole coast line of Christendom, from Gallicia to the Elbe; in 874 they began to colonise Iceland; in 877 they sighted Greenland; in 922 Rolf the Ganger won his "Normandy" from Charles the Simple, by the Treaty of Clair-sur-Epte; as early as 840 was founded the first Norse or Ostman kingdom in Ireland, and in 878 the Norse earldom of the Orkneys, while about the same time the first Vikings seem to have reached the White Sea and the extreme North of Europe.

This advance is almost as rapid as that of the early Saracens; within a hundred years from the first disturbance of Danes and Northmen by the growing, all-including power of the new national kingdoms,—within three generations from Halfdan the Black,—first the flying rebels, and then the royalists in pursuit of them, had reached the farthest western and northern limits of the known world, from Finisterre in "Spanland" to Cape Farewell in Greenland, from the North Cape in Finland to the Northwest Capes of "Irland," from Novgorod or "Holmgard" in Russia to "Valland," between the Garonne and the Loire.

The chief lines of Northern advance were three—by the north-west, south-west, and north-east, but each of these divided, after a time, with important results.

The first sea-path, running by Caithness, Orkneys, Shetlands, and Färoes, reached Iceland, Greenland, and at last Vinland on the North American Continent; but from the settlements on the coasts and islands of northern Scotland, a fresh wave of pirate colonists swept down south-west into the narrow seas of St. George's Channel and beat upon the east and north and south of Ireland and the western coasts of England and of "Bretland."

The second invasion ran along the North German coast, and on reaching the Straits of Dover, fell upon both sides of the English Channel, according as the resistance was stronger or weaker in Wessex or in Frankland. The advanced guard reunited with Ostmen and Orkneyers in the Scilly Isles, and in Cornwall, and pressed on to the plunder of the Bay of Biscay and its coasts. The most restless of all were not long in finding out the wealth of the Moslem Caliphate of Cordova, and trying to force their way up the Douro and the Tagus.