The historian of geology or the theologian may complain that we trespass on their domains in discussing theories of the Creation in a book devoted to the history of geography. Yet this is justifiable if we hold with most modern geographers that some explanation of the immediate causes of existing terrestrial conditions is an essential part of geography. These causes, it was the opinion of medieval thinkers, were to be sought for in the processes of the Creation. No man had the vaguest conception of the countless eons that have elapsed during which air, sea, and land have been in evolution. The good Christian thought that the world was made by God in the course of the six days of Genesis and that it then assumed practically the identical geographical appearance it has preserved ever since. In the Middle Ages geology, geography, and theology were inextricably interwoven. Then again, the geographical lore of the Middle Ages involves a wider range of subjects in space, as well as in time, than is now included in geography. If medieval man had no knowledge of the age of the earth, he also had but the feeblest understanding of the immensity of the universe. To him, earth, stellar bodies, and celestial spheres were all part of a unified system of which the earth formed the core and most important member. Cosmology, astronomy, astrology, theology all dealt with this unified, geocentric, cosmic system; the interrelations between them were immediate and intimate. We cannot avoid some discussion of the matters in which these allied sciences bore directly on geography. ORIGINS OF THE GEOGRAPHICAL LORE OF THE TIME OF THE CRUSADES Whence came the geographical lore of the time of the Crusades? Some of it came from books of earlier ages, some of it from contemporary observation. A sharp distinction may be made between the geography of the scholar and churchman, drawn largely from antiquity, and the geography of the merchant, soldier, and pilgrim, who learned of the world by travel and exploration. It was exceptional when the philosopher or theologian incorporated in his book the reports of recent travels. Indeed, we are almost startled to come across a bit of “up-to-date” geography in the philosophical or theological treatises. Even the histories and chronicles of contemporary events, though perforce containing more new geography than works of deeper learning, tended to appeal to ancient authorities in explaining the course of rivers or the relation of provinces or mountain chains to each other. Any consideration of the state of medieval geography inevitably presupposes some acquaintance with the earlier accumulation of geographical lore from which it borrowed.