Some people held the earth to be hemispherical, and to be supported like a boat turned upside down upon the heads of four elephants, which stood on the back of an immense tortoise. Other primitive ideas represented the earth as a vast plain or flat island, surrounded on all sides by an inaccessible and interminable ocean. At the extremities and around the borders were placed the "fortunate isles," or imaginary regions, peopled by giants, pygmies, and extraordinary beings. The circumscribing water surrounding the irregular outlines of the land led to the idea of a universal ocean. But, when men began to have experience of the sea by early navigation, the idea of a circular horizon always observed led to the notion that the ocean was bounded, and the whole earth came to be represented as contained in a circle, beneath which were roots reaching downward...