<head>I. Some General Remarks. The Subject of this Book.</head>Those who in a general history have dealt separately with the geography of the continents
like Ephorus and Polybius.
Polybius says that in regard to Greece Eudoxus has given a good and Ephorus a very good account of the foundation of cities, genealogies, migrations,
and the planters of colonies; "but I," he adds, "will describe the actual situation of places and give the actual distances, that being the most essential thing in geography."
But yet it is you, Polybius, who introduce the popular misstatements of distances not only outside Greece, but in Greece itself.
Polybius the historian has composed a book with the title On the parts of the globe under the Celestial Equator, that is to say in the middle of the torrid zone.
He says that the region is inhabited, and has a more temperate climate than that of those who inhabit extremities of the torrid zone. On the one hand he cites the accounts given by those who have actually visited the region, and can testify to the fact, and on the other he argues from the nature of the sun's movements.
For at the solstices the sun remains a long time near the tropic circles both in approaching them and receding from them, so that we actually see it stay in their neighbourhood for about forty days; for which reason the length of the day remains almost the same for about forty days.
So owing to the length of its stay over the climates lying under the tropic circles, that region is burnt up and is uninhabitable owing to the excessive heat. But from the equinoctial circle or equator the sun recedes rapidly, so that the length of the day rapidly increases or decreases after the equinoxes.
It is reasonable then to suppose that the climates situated under the equator are more temperate, as the sun does not prolong his stay near the extreme point but rapidly recedes from it. For all those who live between the two tropic circles are equally exposed to the passage of the sun; but he remains longer over those who live under the actual tropics.
So for this reason the region under the equator in the middle of the torrid zone has a more temperate climate than those at the extremities of the torrid zone, which lie under the tropic circles.
Polybius makes the zones six in number, two lying under the arctic circles, two between these and the tropic circles, and two between the latter and the equinoctial circle or equator.
Polybius is mistaken in making some zones determined by the arctic circles, two immediately under them, and two between them and the tropic circles.
But if, as Eratosthenes says, the zone under the equator is temperate, agreeing in this with Polybius — the latter adds that it is very high and therefore has a rainfall, the clouds from the north during the etesian winds being arrested by the heights in large masses — it is much better to assume that this is a third narrow temperate zone, than to introduce here the two zones under the tropic circles.
Poseidonius is against the statement of Polybius that the region under the equator is very high.
Those after Aratus are not at all agreed about the number of the zones. Some, like Polybius and Poseidonius, say they are six, dividing the torrid zone into two.
Walbank Commentary