One of the virtues of Robert Bartlett’s The Natural and the Supernatural in the Middle Ages (aside from a chapter on dogs and dogheads) is his discussion of the medieval puzzle concerning land and sea. By the four-elements theory, earth was the densest element, and thus should gravitate to the lowest point. Why, then, isn’t the world completely covered with water? Why doesn’t the land sink?

Godfrey of St. Victory answers this question with a direct intervention from God: “what nature is it that earth, which is naturally heavier than water, should appear above the water, unless nature had surrended at God’s command?” Things have natural bounds, and transgress those bounds only when the “lord of nature” commands it.

Dante entered the debate, and attempted a natural explanation. As summarized by Bartlett, “the spheres of earth and water do not have a common center but . . . there is a lump or hump in the sphere of the earth, bringing the habitable part of the world above the surface of the water, and the cause of this protruberance is the influence of the stars.”