Library of Congress Geography and Map Division

      Latin for "globe of the world" or, more poetically, "wheel of the world." From ancient times to the Renaissance, this legend was applied to any map of the world, "world" of course meaning "the world as it was known at the Time." This originally included only the Mediterranean Sea and its surrounding territories but later came to cover Asia and the Americas. Many 16th-century maps, and at least one 20th-century wristwatch, are labeled "orbis terrarum."

      The Greeks were aware by 500 BC that the earth is spherical; they even calculated its size, though not all that accurately. Romans required accurate navigation aids and produced practical maps representing the world as a disk with east, or orient, at the top (hence the word "orientation"). Maps by Ptolemy from around AD 150 survive only as medieval copies but seem remarkably accurate.

      In the Middle Ages, from the 7th through 12th centuries, religious mapmakers wished to illustrate a geography of faith rather than mere terrestrial territory. Their "orbis terrarum" maps literally use an O with a T in it -- a circular ocean surrounds the earth, which itself surrounds a T-shaped body of water. (The stem of the T is the Mediterranean, with the crossbar formed by the Hellespont on the left and the Nile on the right.) One extremely simple map drawn by Isidore of Seville in AD 630 follows the O-and-T configuration -- it locates only Jerusalem, Europe, and Africa, and assigns each of the three continents to one of the sons of Noah. Paradise, the most desirable destination, is of course at the top of the map -- just go to Jerusalem, head east, and there you are.