The sixth book contains an explanation of some of the most striking natural appearances, especially thunder, lightning, hail, rain, snow, ice, cold, heat, wind, earthquakes, volcanoes, springs and localities noxious to animal life, which leads to a discourse upon diseases. This introduces a detailed description of the great pestilence that devastated Athens during the Peloponnesian War. With this episode, the book closes; this abrupt ending suggests that Lucretius might have died before he was able to finalize and fully edit his poem.