Lucretius, De rerum natura // This elegant manuscript of Lucretius's philosophical poem, copied by an Augustinian friar for a pope, is an example of the interest in ancient accounts of nature taken by the Renaissance curia. The work, written in the first century B.C., contains one of the principal accounts of ancient atomism. The poem was little known in the Middle Ages and its author dismissed as an atheist and lunatic, but after the discovery of an early manuscript in 1417 by the humanist and papal secretary Poggio Bracciolini, it circulated widely in Italy. This is one of numerous copies made at that time. The coat of arms of Sixtus IV appears on this page.