Medieval T-O Maps and Portolan Charts

The T-O map (orbis terrarum) schematizes the inhabited world as a circle, the "O," divided into three continents by a T-shaped body of water representing the Mediterranean Sea, the Nile, and the Don (Tanais) rivers, a tripartite division tied to the biblical allocation of the earth among Noah's three sons, Shem, Ham, and Japheth. The form was popularized above all by Isidore of Seville's Etymologiae (Book XIV, composed roughly 615–630 CE), and it typically follows the convention of placing East at the top of the map, which is the literal origin of the modern word "orientation," so that Asia occupies the upper half of the circle while Europe and Africa share the lower half; Jerusalem is frequently placed at or near the map's geometric center, reflecting Ezekiel 5:5's description of Jerusalem set "in the midst of the nations."