Some words should perhaps be said on the geographical works of the Arabs. One of the most important of these, by Yacut, is in the form of a huge Gazetteer, arranged in alphabetical order; but the greatest geographical work of the Arabs is by EDRISI, geographer to King Roger of Sicily, 1154, who describes the world somewhat after the manner of Ptolemy, but with modifications of some interest. He divides the world into seven horizontal strips, known as "climates," and ranging from the equator to the British Isles. These strips are subdivided into eleven sections, so that the world, in Edrisi's conception, is like a chess-board, divided into seventy-seven squares, and his work consists of an elaborate description of each of these squares taken one by one, each climate being worked through regularly, so that you might get parts of France in the eighth and ninth squares, and other parts in the sixteenth and seventeenth. Such a method was not adapted to give a clear conception of separate countries, but this was scarcely Edrisi's object. When the Arabs--or, indeed, any of the ancient or mediæval writers--wanted wanted to describe a land, they wrote about the tribe or nation inhabiting it, and not about the position of the towns in it; in other words, they drew a marked distinction between ethnology and geography. [Illustration: THE WORLD ACCORDING TO IBN HAUKAL.] But the geography of the Arabs had little or no influence upon that of Europe, which, so far as maps went, continued to be based on fancy instead of fact almost up to the time of Columbus. Meanwhile another movement had been going on during the eighth and ninth centuries, which helped to make Europe what it is, and extended considerably the common knowledge of the northern European peoples. For the first time since the disappearance of the Phoenicians, a great naval power came into existence in Norway, and within a couple of centuries it had influenced almost the whole sea-coast of Europe. The Vikings, or Sea-Rovers, who kept their long ships in the _viks_, or fjords, of Norway, made vigorous attacks all along the coast of Europe, and in several cases formed stable governments, and so made, in a way, a sort of crust for Europe, preventing any further shaking of its human contents. In Iceland, in England, in Ireland, in Normandy, in Sicily, and at Constantinople (where they formed the _Varangi_, or body-guard of the Emperor), as well as in Russia, and for a time in the Holy Land, Vikings or Normans founded kingdoms between which there was a lively interchange of visits and knowledge.