In describing the universe the philosophers mention five circles, which the Greeks call παράλληλοι that is, zones, into which the circle of lands is divided.... Now let us imagine them after the manner of our right hand, so that the thumb may be called the Arctic circle, uninhabitable because of cold; the second, the summer circle, temperate, inhabitable; the middle (finger), the equinoctial (_Isemerinus_) circle, torrid, uninhabitable; the fourth, the winter circle, temperate, inhabitable; the fifth, the Antarctic circle, frigid, uninhabitable. The first of these is the northern, the second, the solstitial, the third, the equinoctial, the fourth, the winter circle, the fifth, the southern.... The following figure shows the divisions of these circles. (Fig. 1.) Now, the equinoctial circle is uninhabitable because the sun, speeding through the midst of the heaven, creates an excessive heat in these places, so that, on account of the parched earth, crops do not grow there, nor are men permitted to dwell there, because of the great heat. But, on the other hand, the northern and southern circles, _being adjacent to each other_, are not inhabited, for the reason that they are situated far from the sun’s course, and are rendered waste by the great rigor of the climate and the icy blasts of the winds. But the circle of the summer solstice which is situated _in the east, between the northern circle and the circle of heat_, and the circle which is placed _in the west, between the circle of the heat and the southern circle_, are temperate for the reason that they derive cold from one circle, heat from the other. Of which Virgil [says]: “Between these and the middle [zone] two are granted to wretched mortals by the gift of the gods.” Now, they who are next to the torrid circle are the Ethiopians, who are burnt by excessive heat.[61] [61] De Quinque Circulis. “In definitione autem mundi circulos aiunt philosophi quinque, quos Graeci παραλλήλους—id est, zonas—vocant, in quibus dividitur orbis terrae.... Sed fingamus eas in modum dextrae nostrae, ut pollex sit circulus ἀρτικός, frigore inhabitabilis; secundus circulus θερινὸς, temperatus habitabilis; medius circulus ἰσημερινὸς, torridus inhabitabilis; quartus circulus χειμερινὸς, temperatus habitabilis; quintus circulus ἀνταρτικὸς, frigidus inhabitabilis. Horum primus septentrionalis est, secundas solstitialis, tertius aequinoctialis, quartus hiemalis, quintus australis.... “Quorum circulorum divisiones talis distinguit figura (Fig. I).