The men who have written best concerning the nature of the earth, following the guidance of Isidore and other learned men,[230] state that there are certain zones on the heavens under which men cannot live. One is very hot and, because of the glowing heat which burns everything that comes beneath it, people cannot exist under this zone. It seems reasonable that this is the broad path of the sun, and I believe it is because this zone is pervaded with the sun’s flaming rays that no one who wishes only a moderately warm dwelling place can live beneath it. These writers have also said concerning two other zones in the sky that under them too the land is uninhabitable; because, on account of their frigidity, it is no more comfortable to dwell under them than under the first mentioned where the heat is torrid. For there the cold has developed such a power that water casts aside its nature and turns into ice masses; in this way all those lands become ice-cold, and the seas too, that lie under either of these two zones. From this I conclude that there are five zones in the heavens: two under which the earth is habitable, and three under which it is uninhabitable. Footnote 230: Isidore of Seville (d. 636) discusses the five zones in his _Etymologiae_, iii, c. xliv; xiii, c. vi; and in his _De Natura Rerum_, c. x. The editors of the Sorö edition suggest that the “other learned men” may be Macrobius and Martianus Capella, the famous encyclopedists of the fifth century (p. 195). But as these writers preceded Isidore by nearly two centuries, it is unlikely that their works were more than indirect sources for the scientific statements in the _Speculum Regale_. It is more probable that the reference is to such writers as Bede, Rabanus Maurus, and Honorius of Autun, though it is impossible to specify what authority was followed. Now all the land that lies under the zones between the hot and the cold belts can be occupied; but it is likely that owing to location the lands differ somewhat, so that some are hotter than others; the hottest being those that are nearest the torrid belt. But lands that are cold, like ours, lie nearer the frigid zones, where the frost is able to use its chilling powers. Now in my opinion it seems most probable that the hot zone extends from east to west in a curved ring like a flaming girdle around the entire sphere. On the other hand, it is quite probable that the cold zones lie on the outer edges of the world to the north and south: and in case I have thought this out correctly, it is not unlikely that Greenland lies under the frigid belt; for most of those who have visited Greenland testify that there the cold has received its greatest strength. Moreover, both sea and land bear testimony in their very selves that there the frost and the overpowering cold have become dominant, for both are frozen and covered with ice in summer as well as in winter.