Geography

​Polybius, on the one hand, is not right in making certain zones defined by the arctic circles, namely, two falling under them and two between them and the tropics; for it has been said that what is immutable must not be defined by mutable signs. Nor should the tropics be used as boundaries of the scorched zone; and this too has been said. However, in dividing the scorched zone in two, he seems to have been prompted by no mean idea, in accordance with which we also naturally divide the whole earth in two, into the northern and southern hemispheres, by the equator. For it is clear that the scorched zone is also divided along this line of division, and this produces a certain suitability, so that each hemisphere is composed of three complete zones of like kind with those in the other. Now, such a division admits the partition into six zones, but the other does not at all. If, for example, you were to cut the earth in two by the circle passing through the poles, you would not reasonably cut each of the hemispheres, the western and the eastern, into six zones, but the division into five would be sufficient. For the fact that both parts of the scorched zone, which the equator makes, have the same character and lie adjacent to each other makes the division superfluous and redundant, whereas the temperate and frozen zones, though of like kind in both hemispheres, do not lie adjacent to each other; thus, you would also sufficiently divide into five the whole earth when conceived as made up of such hemispheres. But if, as Eratosthenes says, the region falling under the equator is temperate, as Polybius also agrees (and the latter adds also that it is because it is highest; for which reason it is also subject to heavy rains, since the greatest number of northern clouds during the Etesian winds collide there with the high lands), it would be much better to make this a third, narrow temperate zone, rather than to introduce those under the tropics. And such facts as Posidonius also mentions support these views: namely, that there the shifts of the sun to the sides are swifter, and likewise its passage from east to west; for of motions of equal speed, those along a great circle are swifter.

​But Posidonius objects to Polybius because the latter says that the inhabited region under the equator is the highest; for on a spherical surface there is no height because of its smoothness, nor indeed is the region under the equator mountainous, but rather a plain level with the surface of the sea, and the rains that fill the Nile come from the Ethiopian mountains. And yet, having said these things here, in other passages he concedes the point, saying that he suspects there are mountains under the equator, against which the clouds, colliding from both temperate zones on either side, produce the rains. Now this contradiction is obvious; but even granting that the region under the equator is mountainous, another difficulty would seem to arise; for the same writers say that the ocean is continuous. How, then, do they place mountains in the middle of it? Unless, indeed, they mean to speak of certain islands. But however this may be, it falls outside the province of geography; and we should perhaps allow him who has proposed a treatise on the ocean to examine these matters.