To the people who lived four centuries ago in Europe only a very small portion of the earth's surface was known. Their geography was confined to the regions lying immediately around the Mediterranean, and including Europe, the north of Africa, and the west of Asia. Round these there was a margin, obscurely and imperfectly described in the reports of merchants; but by far the greater part of the world was utterly unknown. Great realms of darkness stretched all beyond, and closely hemmed in the little circle of light. In these unknown lands our ancestors loved to picture everything that was strange and mysterious. They believed that the man who could penetrate far enough would find countries where inexhaustible riches were to be gathered without toil from fertile shores, or marvellous valleys; and though wild tales were told of the dangers supposed to fill these regions, yet to the more daring and adventurous these only made the visions of boundless wealth and enchanting loveliness seem more fascinating.