In its earlier stages, then, the history of geographical discovery is mainly a history of conquest, and what we shall have to do will be to give a short history of the ancient world, from the point of view of how that world became known. "Became known to whom?" you may ask; and we must determine that question first. We might, of course, take the earliest geographical work known to us--the tenth chapter of Genesis--and work out how the rest of the world became known to the Israelites when they became part of the Roman Empire; but in history all roads lead to Rome or away from it, and it is more useful for every purpose to take Rome as our centre-point. Yet Rome only came in as the heir of earlier empires that spread the knowledge of the earth and man by conquest long before Rome was of importance; and even when the Romans were the masters of all this vast inheritance, they had not themselves the ability to record the geographical knowledge thus acquired, and it is to a Greek named Ptolemy, a professor of the great university of Alexandria, to whom we owe our knowledge of how much the ancient world knew of the earth. It will be convenient to determine this first, and afterwards to sketch rapidly the course of historical events which led to the knowledge which Ptolemy records. In the Middle Ages, much of this knowledge, like all other, was lost, and we shall have to record how knowledge was replaced by imagination and theory. The true inheritors of Greek science during that period were the Arabs, and the few additions to real geographical knowledge at that time were due to them, except in so far as commercial travellers and pilgrims brought a more intimate knowledge of Asia to the West. The discovery of America forms the beginning of a new period, both in modern history and in modern geography. In the four hundred years that have elapsed since then, more than twice as much of the inhabited globe has become known to civilised man than in the preceding four thousand years. The result is that, except for a few patches of Africa, South America, and round the Poles, man knows roughly what are the physical resources of the world he inhabits, and, except for minor details, the history of geographical discovery is practically at an end.