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), is a type of medieval world map, sometimes also called a Beatine map or a Beatus map because one of the earliest known representations of this sort is attributed to Beatus of Liébana, an 8th-century Spanish monk. The map appeared in the prologue to his twelve books of commentaries on the Apocalypse.

The T-O map represents the physical world as first described by the 7th-century scholar Isidore of Seville in his Etymologiae (chapter 14, de terra et partibus):

Latin: Orbis a rotunditate circuli dictus, quia sicut rota est [...] Undique enim Oceanus circumfluens eius in circulo ambit fines. Divisus est autem trifarie: e quibus una pars Asia, altera Europa, tertia Africa nuncupatur.

English: The [inhabited] mass of solid land is called round after the roundness of a circle, because it is like a wheel [...] Because of this, the Ocean flowing around it is contained in a circular limit, and it is divided in three parts, one part being called Asia, the second Europe, and the third Africa.

Although Isidore taught in the Etymologiae that the Earth was "round", his meaning was ambiguous and some writers think he referred to a disc-shaped Earth. However, other writings by Isidore make it clear that he considered the Earth to be globular. Indeed, the theory of a spherical earth had always been the prevailing assumption among the learned since at least Aristotle, who had divided the spherical earth into zones of climate, with a frigid clime at the poles, a deadly torrid clime near the equator, and a mild and habitable temperate clime between the two.

The T and O map represents only the one half of the spherical Earth. It was presumably considered a convenient projection of known-inhabited parts, the northern temperate half of the globe. Since the southern temperate clime was considered uninhabited, or unattainable, there was no need to depict them on a world map. It was then believed that no one could cross the torrid equatorial clime and reach the unknown lands on the other half of the globe. These imagined lands were called antipodes.

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