How did a lost Roman poem resurface in a German monastery in 1417?

A clerk in papal service with time on his hands found it. In January 1417 Poggio Bracciolini, a Florentine whose duties had taken him to the Council of Constance, rediscovered De rerum natura, a Roman poem by Lucretius of some 7,400 lines in six books, probably in the Benedictine library at Fulda. He had spent his forced leisure exploring the libraries of Swiss and Swabian abbeys, and he recognised the author's name because he remembered it as quoted by Cicero.

The poem set out Epicurean philosophy. Epicurus had blamed human unhappiness largely on dread of the gods' power and wrath, and made it his mission to remove those fears; Lucretius argued that the world's workings result from regular but purposeless motions of tiny atoms in empty space. He did not deny that gods exist, only that they made the universe, care about human affairs or intervene in the world. Some Christian apologists later read it as an atheist manifesto.

Poggio's manuscript is lost, but it spread. The copy made by his friend Niccolò de' Niccoli, in his renowned book hand, became the model for more than fifty other copies, and Poggio later complained that Niccoli had not returned the original for 14 years. The poem was first printed in 1473.

Was it truly lost? Not entirely. A handful of references survive from the ninth to the fifteenth centuries, and Guido Billanovich showed that Paduan pre-humanists knew the whole poem in the thirteenth century. Stephen Greenblatt's 2011 book The Swerve, which won a Pulitzer Prize, argues that Poggio's discovery reintroduced ideas that sparked the modern age, but the historian John Monfasani found that interpretation "questionable" and "unwarranted".