Within forty years the map of Africa, which was practically a blank in the interior, and, as will be shown, was better known in 1680 than in 1850, has been filled up almost completely by researches due to motives of conquest, of trade, or of scientific curiosity.
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.