T and O map

A T and O map or O–T or T–O map (orbis terrarum, orb or circle of the lands; with the letter T inside an O), also known as an Isidoran map, is a type of early world map that represents the Afro-Eurasian landmass as a circle (= O) divided into three parts by a T-shaped combination of the Mediterranean sea, the river Tanais (Don) and the Nile. The origins of this diagram are contested, with some scholars hypothesizing an origin in Roman or late antiquity, while others consider it to have originated in 7th- or early 8th-century Spain.

The earliest surviving example of a T-O map is found in a late 7th- or early 8th-century copy of Isidore of Seville's (c. 560 – 636) De natura rerum, which alongside his Etymologiae (c. 625) are two of the most common texts to be accompanied by such a diagram in the Middle Ages. A later manuscript added the names of Noah's sons (Sem, Iafeth and Cham) for each of the three continents (see Biblical terminology for race). A later variation with more detail is the Beatus map drawn by Beatus of Liébana, an 8th-century Spanish monk, in the prologue to his Commentary on the Apocalypse.

Relevant textual descriptions of the world

The earliest T-O maps are closely associated with two sections of the work of Isidore of Seville:

De Natura Rerum 48.2-3 (drawn verbatim from Hyginus' De astronomia 1.9(8) and Augustine of Hippo's City of God 16.17):

So the earth may be divided into three sides (trifarie), of which one part is Europe, another Asia, and the third is called Africa. Europe is divided from Africa by a sea from the end of the ocean and the Pillars of Hercules. And Asia is divided from Libya with Egypt by the Nile... Moreover, Asia – as the most blessed Augustine said – runs from the southeast to the north ... Thus we see the earth is divided into two to comprise, on the one hand, Europe and Africa, and on the other only Asia.