The Antipodes and Inhabitable Zones

Once the Greeks accepted that the earth was a sphere, a startling consequence followed: the surface must divide into climatic belts, with a scorching equatorial zone presumed too hot to cross and temperate bands on either side. This raised the haunting possibility of "antipodeans" — people living on the far side of the globe with their feet pointed opposite to ours, forever sealed off from the known inhabited world by the impassable torrid zone. Plato had already argued that on a sphere there is no absolute "up" or "down," dissolving the objection that such people would fall off, while later geographers like Crates of Mallus mapped the earth into multiple inhabited patches. Cicero gave the idea its most famous expression in the Dream of Scipio, where the cosmos is viewed from above and the human oikoumenē shrinks to a few scattered specks.