Geography

​For one must assume that the heaven is divided into five zones, and the earth likewise into five zones, and that the zones below are homonymous with those above; and we have already stated the reasons for the division into zones. These zones would be defined by circles drawn parallel to the equator on either side of it, two of them enclosing the scorched zone, and two following after these, which create the two temperate zones adjacent to the scorched zone, and the frigid zones adjacent to the temperate zones. Under each of the heavenly circles lies the circle on earth homonymous with it, and the zone likewise under the zone. Now they say that the temperate zones are capable of being inhabited, but the others are uninhabitable, one because of heat and the others because of cold. In the same manner also concerning the tropics and the polar circles, among those for whom polar circles exist, they define them by making those on earth homonymous with those above, and also those lying under each of them. Since the equator cuts the whole heaven in half, the earth also must necessarily be divided by the equator upon it. And each of the hemispheres both of the heaven and of the earth is called, the one northern, the other southern; and so, with the scorched zone also being cut in half by the same circle, one part of it will be northern, the other southern; and it is clear that also of the temperate zones, the one will be northern and the other southern, homonymously with the hemisphere in which it lies. And the northern hemisphere is called that which contains that temperate zone in which, to one looking from the east toward the west, the pole is on the right and the equator on the left, or in which, to those looking toward the south, the west is on the right and the east on the left, while the southern is that which is in the opposite state; so that it is clear that we are in one of the two hemispheres, and indeed in the northern one, and it is not possible to be in both; for in the middle are great rivers, first Oceanus, then the scorched zone. And neither is there Oceanus in the middle of our inhabited world cutting it as a whole, nor indeed a scorched region; nor indeed is any part of it found to have climates opposite to those described in the northern temperate zone.

​The geometer, then, taking these things and further employing the things demonstrated by the astronomer—among which are found both the circles parallel to the equator for each habitation and those cutting these at right angles, being drawn through the poles—measures the habitable earth by traveling through it, and the rest from the ratio of distances. In this way he would find how great the distance is from the equator to the pole, which is a quadrant of the greatest circle of the earth; and having this, he also has its fourfold, which is the circumference of the earth. Just as, therefore, the one who measured the earth received his principles from the astronomer, and the astronomer from the physicist, in the same way the geographer also must start from the one who has measured the whole earth, believing him and those whom he believed, and first set forth how large our inhabited world is, what its shape is, and what its nature is and how it stands in relation to the whole earth (for this is peculiar to the geographer), and then make the fitting account concerning the particulars both on land and on sea, pointing out whatever has not been adequately stated by our predecessors who are believed to have been the best in these matters.