Posidonius informs us that Parmenides was the first to make this division of the earth into five zones, but that he almost doubled the size of the torrid zone, which is situated between the tropics, by bringing it beyond these into the temperate zones. But according to Aristotle the torrid zone is contained between the tropics, the temperate zones occupying the whole space between the tropics and the arctic circles. Both of these divisions Posidonius justly condemns, for the torrid zone is properly the space rendered uninhabitable by the heat. Whereas more than half of the space between the tropics is inhabited, as we may judge by the Ethiopians who dwell above Egypt.
Posidonius, who himself divides the earth into zones, tells us that “five is the number best suited for the explanation of the celestial appearances, two of these are periscii, which reach from the poles to the point where the tropics serve for Arctic Circles; two more are heteroscii, which extend from the former to the inhabitants of the tropics, and one between the tropics, which is called amphiscius, but for matters relative to the earth, it is convenient to suppose two other narrow zones placed under the tropics, and divided by them into two halves, over which [every year] for the space of a fortnight, the sun is vertical.” These zones are remarkable for being extremely arid and sandy, producing no vegetation with the exception of silphium, and a parched grain somewhat resembling wheat. This is caused by there being no mountains to attract the clouds and produce rain, nor any rivers flowing through the country. The consequence is that the various species are born with woolly hair, crumpled horns, protruding lips, and wide nostrils; their extremities being as it were gnarled. Within these zones also dwell the Ichthyophagi. He further remarks, that these peculiarities are quite sufficient to distinguish the zones in question: those which are farther south having a more salubrious atmosphere, and being more fruitful and better supplied with water. (The Geography of Strabo, I, ii, 2, 3)