The work of Claudius Ptolemy sums up to us the knowledge that the Romans had gained by their inheritance, on the western side, of the Carthaginian empire, and, on the eastern, of the remains of Alexander's empire, to which must be added the conquests of Cæsar in North-West Europe. Cæsar is, indeed, the connecting link between the two shells that had been growing throughout ancient history. He added Gaul, Germany, and Britain to geographical knowledge, and, by his struggle with Pompey, connected the Levant with his northerly conquests. One result of his imperial work must be here referred to. By bringing all civilised men under one rule, he prepared them for the worship of one God. This was not without its influence on travel and geographical discovery, for the great barrier between mankind had always been the difference of religion, and Rome, by breaking down the exclusiveness of local religions, and substituting for them a general worship of the majesty of the Emperor, enabled all the inhabitants of this vast empire to feel a certain communion with one another, which ultimately, as we know, took on a religious form. The Roman Empire will henceforth form the centre from which to regard any additions to geographical knowledge. As we shall see, part of the knowledge acquired by the Romans was lost in the Dark Ages succeeding the break-up of the empire; but for our purposes this may be neglected and geographical discovery in the succeeding chapters may be roughly taken to be additions and corrections of the knowledge summed up by Claudius Ptolemy. CHAPTER III GEOGRAPHY IN THE DARK AGES We have seen how, by a slow process of conquest and expansion, the ancient world got to know a large part of the Eastern Hemisphere, and how this knowledge was summed up in the great work of Claudius Ptolemy. We have now to learn how much of this knowledge was lost or perverted--how geography, for a time, lost the character of a science, and became once more the subject of mythical fancies similar to those which we found in its earliest stages. Instead of knowledge which, if not quite exact, was at any rate approximately measured, the mediæval teachers who concerned themselves with the configuration of the inhabited world substituted their own ideas of what ought to be.[1] This is a process which applies not alone to geography, but to all branches of knowledge, which, after the fall of the Roman Empire, ceased to expand or progress, became mixed up with fanciful notions, and only recovered when a knowledge of ancient science and thought was restored in the fifteenth century. But in geography we can more easily see than in other sciences the exact nature of the disturbing influence which prevented the acquisition of new knowledge. [Footnote 1: It is fair to add that Professor Miller's researches have shown that some of the "unscientific" qualities of the mediæval _mappoe mundi_ were due to Roman models.]