The Almagest and the Geography, the two scientific masterpieces of Claudius Ptolemy (2nd century), guided the progress of astronomical and geographical studies throughout the Renaissance. The Almagest, which had been known since the Middle Ages through the mediation of Islamic astronomers, furnished a mathematical explanation of the geocentric system. The Geography was rediscovered in the Western World only near the end of the 14th century, thanks to a Greek codex brought to Florence by the erudite Byzantine Emanuele Crisolora (1350-1415). This work contained a description of the known world at the time of Ptolemy as well as an explanation of the projective methods necessary to construct a world map and regional charts. The diligent updating of Ptolemy’s geographical data carried out by map-makers and commentators in the 15th century favored studies that led to the discovery of the New World, an epochal event to which such eminent Florentines as Paolo dal Pozzo Toscanelli (1397-1482) and Amerigo Vespucci (1454-1512) contributed.