The terms antipodes and antichthones, along with others such as antoikoi and perioikoi, referred to hypothetical peoples dwelling beyond the extent of the known world. These terms were the product of a mathematically based astronomy in which the spherical nature of the Earth was a fundamental element. Calculations of the size of the Earth resulted in the conjecture that inhabited land existed beyond the known world of Asia, Europe, and Africa/Libya. Such land was usually thought to be inaccessible owing to the expanse of Ocean, or because of the extremes of heat and cold found, respectively, at the Equator and the poles.The concept of the antipodes appears to have emerged from Pythagorean thought. Pythagoras was credited with the doctrine that inhabitation was not restricted to the known world, and specifically that there were inhabitants on the opposite side of the Earth, whose “down” was “up” for those in the known world; certain Pythagoreans conceived of an antichthon, or counter-Earth, in relation to the known world (Diog. Laert., Vitae Philosophorum 8.