the other half of the Martian year. In addition, unlike what one would expect at the south pole of Mars, the temperature in the Valley of Dor is mild and temperate, and although that may be accounted for by its being in a deep crater, the temperature in the Therns' fortress on the surrounding cliffs does not appear to be all that cold either. World of Barsoom A million years before the narrative commences, Mars was a lush world with oceans. As the oceans receded, and the atmosphere grew thin, the planet has devolved into a landscape of partial barbarism; living on an aging planet, with dwindling resources, the inhabitants of Barsoom have become hardened and warlike, fighting one another to survive. Barsoomians distribute scarce water supplies via a worldwide system of canals, controlled by quarreling city-states. The thinning Martian atmosphere is artificially replenished from an "atmosphere plant". Themes Race Race is a major theme in the Barsoom novels. It is a world with clear territorial divisions between White, Yellow, Black, Red and Green skinned races. Each has particular traits and qualities, which seem to define the characters of almost every individual thereof. Nevertheless Burroughs' concept of race, as depicted in the novels, is more like a division between species than between ethnicity. The first book, A Princess of Mars, introduced the tall, gangly, four-armed, orc-like Green Martians and the more common humanoid Red Martians. John Carter spent his first ten years on Mars without knowing of the existence of the other races, aside from ancient paintings and frescoes that depicted White Martians. The Gods of Mars introduces two new races; the White-Skinned Therns and the Black-Skinned First Born, both of which are strongly connected to the Martian religion that John Carter exposed in the novel. Both are humanoid like the Reds, and indeed the Therns are close enough to whites on Earth that Carter was able to pose as one, and was easily mistaken for one. Therns The Therns are white skinned and bald, wearing blond wigs. They live in a well-fortified complex of gardens and temples in the cliffs above the Valley Dor, the supposed Martian heaven; the cliffs also contain a network of caves and passages. The Therns control the dangerous beasts that live in the valley, and ransack, enslave, or eat the flesh of the survivors. They consider themselves a unique creation, different from other Martians.