We saw in Chapter I that ancient astronomers had drawn imaginary circles around the terrestrial sphere corresponding to the circles of the heavens and had designated these lines as the boundaries of zones on the earth’s surface.[693] The classical theory of five zones, divided from each other by parallels of latitude, was accepted by the geographical writers of the twelfth and early thirteenth centuries, although, as in classical times, opinions diverged widely regarding the characteristics of each zone. All, however, believed that the two polar caps were cold and that the equatorial regions were hot. For example Bernard Sylvester says in his _De mundi universitate_:[694] Nous, or Providence, “encompassed the earth with five parallels; on the one hand the extremes are frozen, on the other the central portions are hot. Also she made temperate two zones by placing on both sides of them the coldness of the extremities and the course of the sun over the midst of the earth.” UNINHABITABILITY OF POLAR CAPS AND EQUATORIAL ZONE Furthermore, a widely prevalent but not universal theory made the polar caps and equatorial zones not only cold and hot but also uninhabitable. The author of the _De imagine mundi_[695] and Gervase of Tilbury[696] plagiarized what Isidore had written on this subject.[697] They called the five circles separating the zones and the zones themselves from north to south, respectively, _septentrionalis_ (our Arctic Circle and North Polar zone), _solstitialis_ (our Tropic of Cancer and North Temperate zone), _equinoctialis_ (our Equator and Torrid zone), _brumalis_—or _hyemalis_ according to Gervase—(our Tropic of Capricorn and South Temperate zone), and finally _australis_ (our Antarctic Circle and South Polar zone). Of these they thought that only _solstitialis_ was habitable. William of Conches likewise believed[698] in uninhabitable torrid and frigid zones, though he rejected the theory that in the heavens above the sphere of the moon there are qualities of heat and cold corresponding to those of the terrestrial zones. AUSTRAL CONTINENT AND ANTIPODAL REGIONS