In the four corners of the map, alongside the diagrams of the heavens, the four elements, the celestial orbits, and a Garden of Eden illuminated by Leonardo Bellini (active ca. 1443-ca. 1490), Fra Mauro (active ca. 1430-ca. 1459/1464) discusses several key problems in natural philosophy: the number of heavens according to theologians; the distances between the planets; the causes of the tides; why the land emerged from the sea; the absolute and comparative dimensions of the four elements; the extent of habitable lands on the Earth; and the geographic location of Eden.
These seven “rubrics” constitute a sort of treatise on the cosmos surrounding the oikumene, the inhabited and habitable parts of Earth. The inclusion of these topics distinguishes Fra Mauro’s world map both from those of the Middle Ages and of his contemporaries. The world of Fra Mauro is a synthesis of cosmological concepts taken from the natural philosophy of Aristotle (384-322 BCE) and the astronomic texts of Ptolemy (ca. 100-ca. 178), which are summarized and explained in interpretations derived from the De sphaera by John of Holywood (ca. 1195-1256) and the works of the principal scholastic philosophers. Writing in vernacular Venetian, Fra Mauro addresses his observations not to “ecclesiastics” and “authorities”, but rather to the same readers to whom Dante (1265-1321), 150 years earlier, had addressed his pioneering encyclopedia in vernacular Tuscan, the Convivio (The Banquet). He was speaking, that is, to men who, as the great poet said, might not be conversant in Latin, but still wished to satisfy their “human hunger” for knowledge.