The contemporaries of Hildegard who provide the closest analogy to her are Elizabeth of Schönau (died 1165), whose visions are recounted in her life by Eckbertus;[50] and Herrade de Landsberg, Abbess of Hohenburg in Alsace, the priceless MS. of whose _Hortus Deliciarum_ was destroyed by the Germans in the siege of Strasbourg in 1870.[51] With Elizabeth of Schönau, who lived in her neighbourhood, Hildegard was in frequent correspondence. With Herrade she had, so far as is known, no direct communication; but the two were contemporary, lived not very far apart, and under similar political and cultural conditions. Elizabeth’s visions present some striking analogies to those of Hildegard, while the figures of Herrade, of which copies have fortunately survived, often suggest the illustrations of the Wiesbaden or of the Lucca MSS. VI. THE STRUCTURE OF THE MATERIAL UNIVERSE To the student of the history of science, Hildegard’s beliefs as to the nature and structure of the universe are among the most interesting that she has to impart. Her earlier theories are in some respects unique among mediaeval writers, and we possess in the Wiesbaden Codex B a diagram enabling us to interpret her views with a definiteness and certainty that would otherwise be impossible. Hildegard’s universe is geocentric, and consists of a spherical earth,[52] around which are arranged a number of concentric shells or zones. The inner zones are spherical, the outer oval, and the outermost of all egg-shaped, with one end prolonged and more pointed than the other (Fig. 2). The concentric structure is a commonplace of mediaeval science, and is encountered, for instance, in the works of Bede, Isidore, Alexander of Neckam, Roger Bacon, Albertus Magnus, and Dante. To all these writers, however, the universe is spherical. The egg-shape is peculiar to Hildegard. Many of the _Mappaemundi_ of the Beatus and other types exhibit the _surface_ of the habitable earth itself as oval, and it was from such charts that Hildegard probably gained her conception of an oval universe. In her method of orientation also she follows these maps, placing the east at the top of the page where we are accustomed to place the north.[53] It is unfortunate that she does not deal with geography in the restricted sense, and so we are not in full possession of her views on the antipodes, a subject of frequent derision to patristic and of misconception to scholastic writers. She does, however, vaguely refer to the inversion of seasons and climates in the opposite hemisphere,[54] though she confuses the issue by the adoption of a theory widespread in the Middle Ages and reproduced in the _Divina Commedia_, that the antipodean surface of the earth is uninhabitable, since it is either beneath the ocean or in the mouth of the Dragon[55] (Plate XI, cp. Fig. 4). The nature of the antipodean inversion of climates was clearly grasped by her contemporary, Herrade de Landsberg (Fig. 5).