The Figure of the Earth in Isidore's "De natura rerum"

D uring the Hellenistic, Roman, and medieval periods, descriptive literature concerning the cosmos almost uniformly discussed the earth as a globe and the heavens as a sphere.' This literature, often intended for school instruction, was sometimes accompanied by stylized diagrams depicting the globe. The diagrams are of three types: the globe divided both horizontally and vertically into four parts by waters and their projections; the globe with parallel lines representing three, five, or more zones of klima (or latitude); and the globe with the three partially known continents of the oikoumene extended over the entire surface.2 Such diagrams may be inferred from early texts in various languages and from various periods, but with the Babylonian exception mentioned later, the diagrams themselves do not survive until examples belonging to the seventh, eighth, and ninth centuries of our own era. The earliest extant diagram of the earth as a globe occurs in manuscripts of the De natura rerum by Isidore of Seville, a schoolbook intended to outline the organized knowledge proper for an educated man in seventh-century Visigothic Spain. It is a diagram of the third type, known as rota terrarum or orbis terrae. Inexplicably, given its importance, it has suffered comparative neglect, as a brief comparison of its place in the manuscript tradition with its recent publishing history will make clear. The neglect may relate to two problems-the assumption that Isidore did not conceive of the world as a sphere, and the assumption that the rota represents a disk and not a sphere. The rota terrarum however displays a more sophisticated conception of the world than has often been acknowledged. Occurrences of reversed rotae in some of the later English manuscripts of De natura rerum and other Latin works have similarly been ascribed to error. A reconsideration of the Isidorean rota in the context of Greco-Roman depictions of the globe should correct these misapprehensions.