By chance, copies of “On the Nature of Things” somehow made it into a few monastery libraries, places that had buried, seemingly forever, the principled pursuit of pleasure. By chance, a monk laboring in a scriptorium somewhere or other in the ninth century copied the poem before it moldered away. And, by chance, this copy escaped fire and flood and the teeth of time for some five hundred years until, one day in 1417, it came into the hands of a man who proudly called himself Poggius Florentinus, Poggio the Florentine.

Poggio was, among other things, famous for the elegance of his script and for writing the best-known jokebook of its age, a chronicle of cynical tricksters, bawdy friars, unfaithful wives, and foolish husbands. He had served a succession of Roman Pontiffs as a scriptor—that is, a writer of official documents in the Papal bureaucracy—and, through adroitness and cunning, he had risen to the coveted position of Apostolic Secretary. He had access, as the very word “secretary” suggests, to the Pope’s secrets. But above all he was a book hunter, perhaps the greatest of his kind.

Italians had been obsessed with book hunting ever since the poet and scholar Petrarch brought glory on himself around 1330 by piecing together Livy’s monumental “History of Rome” and finding forgotten masterpieces by Cicero and Propertius. Petrarch’s achievement had inspired others to seek out lost classics that had been lying unread, often for centuries. The recovered texts were copied, edited, commented upon, and eagerly exchanged, conferring distinction on those who had found them and forming the basis for what became known as the “study of the humanities.” The “humanists,” as those who were devoted to this study were called, knew from carefully poring over the texts that had survived from classical Rome that many once famous books or parts of books were still missing.

As a humanist, Poggio had quite a few accomplishments. He uncovered an epic poem on the struggle between Rome and Carthage; the works of an ancient literary critic who had flourished during Nero’s reign and had written notes and glosses on classical authors; another critic who quoted extensively from lost epics written in imitation of Homer; a grammarian who wrote a treatise on spelling; a large fragment of a hitherto unknown history of the Roman Empire written by a high-ranking officer in the imperial Army, Ammianus Marcellinus. His salvaging of the complete text of the rhetorician Quintilian changed the curriculum of law schools and universities throughout Europe, and his discovery of Vitruvius’ treatise on architecture transformed the way buildings were designed. But it was in January, 1417, when Poggio found himself in a monastery library, that he made his greatest discovery. He put his hands on a long poem whose author he may have recalled seeing mentioned in other ancient works: “T. LUCRETI CARI DE RERUM NATURA.”

“On the Nature of Things,” by Titus Lucretius Carus, is not an easy read. Totalling seventy-four hundred lines, it is written in hexameters, the standard unrhymed six-beat lines in which Latin poets like Virgil and Ovid, imitating Homer’s Greek, cast their epic poetry. Divided into six untitled books, the poem yokes together moments of intense lyrical beauty; philosophical meditations on religion, pleasure, and death; and scientific theories of the physical world, the evolution of human societies, the perils and joys of sex, and the nature of disease. The language is often knotty and difficult, the syntax complex, and the over-all intellectual ambition astoundingly high.

The stuff of the universe, Lucretius proposed, is an infinite number of atoms moving randomly through space, like dust motes in a sunbeam, colliding, hooking together, forming complex structures, breaking apart again, in a ceaseless process of creation and destruction. There is no escape from this process. When we look up at the night sky and marvel at the numberless stars, we are not seeing the handiwork of the gods or a crystalline sphere. We are seeing the same material world of which we are a part and from whose elements we are made. There is no master plan, no divine architect, no intelligent design. Nature restlessly experiments, and we are simply one among the innumerable results: “We are all sprung from celestial seed; all have that same father, from whom our fostering mother earth receives liquid drops of water, and then teeming brings forth bright corn and luxuriant trees and the race of mankind, brings forth all the generations of wild beasts, providing food with which all nourish their bodies and lead a sweet life and beget their offspring.”

All things, including the species to which we belong, have evolved over vast stretches of time. The evolution is random, though in the case of living organisms it involves a principle of natural selection. That is, species that are suited to survive and to reproduce successfully endure, at least for a time; those which are not so well suited die off quickly. Other species existed and vanished before we came onto the scene; our kind, too, will vanish one day. Nothing—from our own species to the sun—lasts forever. Only the atoms are immortal.

In a universe so constituted, Lucretius argued, it is absurd to think that the earth and its inhabitants occupy a central place, or that the world was purpose-built to accommodate human beings: “The child, like a sailor cast forth by the cruel waves, lies naked upon the ground, speechless, in need of every kind of vital support, as soon as nature has spilt him forth with throes from his mother’s womb into the regions of light.” There is no reason to set humans apart from other animals, no hope of bribing or appeasing the gods, no place for religious fanaticism, no call for ascetic self-denial, no justification for dreams of limitless power or perfect security, no rationale for wars of conquest or self-aggrandizement, no possibility of triumphing over nature. Instead, he wrote, human beings should conquer their fears, accept the fact that they themselves and all the things they encounter are transitory, and embrace the beauty and the pleasure of the world.

Almost nothing is known about the poem’s author, except for a brief biographical sketch by St. Jerome, the great fourth-century Church Father. In the entry for 94 B.C.E., Jerome noted: “Titus Lucretius, poet, is born. After a love-philtre had turned him mad, and he had written, in the intervals of his insanity, several books which Cicero revised, he killed himself by his own hand in the forty-fourth year of his age.” These lurid details have shaped all subsequent representations of Lucretius, including a celebrated Victorian poem in which Tennyson imagined the voice of the mad, suicidal philosopher tormented by erotic fantasies.

Modern scholarship suggests that Jerome’s biographical claims, written more than four centuries after the poet’s death, should be regarded with skepticism. Lucretius’ personal life remains a mystery that no one at this distance is likely to solve. It is possible, however, to know something about his intellectual biography. “On the Nature of Things” is clearly the work of a disciple who is transmitting ideas that had been developed in Greece centuries earlier. Epicurus was Lucretius’ philosophical messiah, and his vision may be traced to a single incandescent idea: that everything that has ever existed and everything that will ever exist is put together out of what the Roman poet called “the seeds of things,” indestructible building blocks, irreducibly small in size, unimaginably vast in number. The Greeks had a word for these invisible building blocks, things that, as they conceived them, could not be divided any further: atoms.