Cosmography Beyond the Earth

Many medieval maps depict the universe as a finite, enclosed space. The earth is located at the center of the universe, while heavenly bodies move around it in circular orbits of increasing size.

In his encyclopedia Imago mundi, Honorius Augustodunensis (ca. 1080-ca. 1140), a Christian theologian, describes the shape of the world as similar to an egg. It has several distinct parts, each enclosed within the next. In this analogy, the heavens are the eggshell surrounding the world. A layer of ether (the egg white) surrounds a layer of turbulent air (the yolk of the egg.) At the center of everything is the earth: the “drop of fat” in the center of the yolk.

De natura rerum, an early encyclopedia by Isidore of Seville (ca. 560-636 CE), contains one such cosmographical diagram. Stars and planets travel along their neatly labeled paths, which are perfectly circular, evenly spaced, and painted in bright colors.

Pierre d'Ailly's Imago mundi, a book of geographical treatises written in the early 15th century, has many similarities to Isidore's diagram. Once again, the universe is a finite space and the earth is a small circle enclosed by the heavens. While Isidore uses circular paths to represent the motion of the heavenly bodies, Pierre's book assigns them their own "spheres," which touch at the edges but do not interact.

The depiction of the cosmos shown in these diagrams is organized, understandable, and pleasing to look at. Isidore and Pierre d'Ailly emphasize the small size of the earth in relation to the vastness of the universe. However, they also provide an explanation of its role in the larger world. The earth is small, but it is far from insignificant.

Sources and Further Reading

Pierre d'Ailly and Jean Gerson. Imago mundi. Madrid: Testimonio Compañía Editorial, 1990. 

E. Edson, E. Savage-Smith. Medieval Views of the Cosmos. Oxford: Bodleian Library, 2004. 

Honorius. Imago mundi, Book One, section I. Trans. by Nicholas Ryan Foster.

Isidore of Seville, Liber astrologicus. Madrid: Millennium Liber, 2013.