T-O maps are maps of the World typical of the period from the 6th -12th centuries. They are so called because of their structure: with the East on top--"oriented"-- they are in the form of a circle with a T in the lower half of the map, with the upright being the Mediterranian Sea the left-hand bar representing the Black Sea, and the right-hand bar, the Nile River. In the center is Jerusalem, and in the uttermost East, the Garden of Eden. Sometimes a red line in the South will serve for the Red Sea; beyond this is a place marked vaguely "southern lands", whose attribution is also sketchy. (Madagascar? Antarctica? Australia? Sudan?) Small islands around the edges represent Ireland, England/Scotland/Wales, and some other, less identifiable features. Straits are shown as large rivers, and mountain ranges as wing-like shapes cutting into the Eurasian landmass. Utterly unusable as navigational aids (the southern coast of the Mediterranian is represented as a straight line), they nonetheless served for many generations the only representation of the world available to the best scholars in Europe.
Philosophically, the map makes sense in the Medieval scheme of things: the Four Elements are represented in their places in harmony, the Fiery South, the cool, earthy North, full of mountains, the watery West, and the windy East, beyond which is Paradise. This map regained some prominence when Umberto Eco used it as the basis for the coded rooms of the Aedificum in The Name of the Rose.