Lucretius (94?-55? bc), Roman poet whose great didactic poem in six books, De Rerum Natura (On the Nature of Things), expounds the philosophical materialism of Greek philosophers Democritus and Epicurus and is the main source for contemporary knowledge of Epicurus's thought. His full name was Titus Lucretius Carus. Lucretius sought to free humanity from the fear of death and of the gods, which he considered the main cause of human unhappiness. His characterization of the universe as a fortuitous aggregation of atoms moving in the void, his insistence that the soul is not a distinct, immaterial entity but a chance combination of atoms that does not survive the body, and his postulation of purely natural causes for earthly phenomena are all calculated to prove that the world is not directed by divine agency and that fear of the supernatural is consequently without reasonable foundation. Lucretius does not deny the existence of gods, but he conceives of them as having no concern with the affairs or destiny of mortals. One of the most famous passages of De Rerum Natura concerns the primitive life of early human beings and the gradual rise of civilization. See also Thematic Essay: Roman Political and Social Thought.