Life is uigilia, wrote C. Plinius Secundus in Historia naturalis (Natural History, pref. 18), by which the old soldier meant that life is being on watch and on duty. The highest duty and the path of divinity was to help one's fellow mortals (HN 2.18, 25.2-3), and Pliny's life, writings, and death were devoted to that end. Although most of his works were lost in the collapse of the western Roman Empire, his surviving work, the Historia naturalis, is one of the largest works to survive from antiquity and was the standard encyclopedia of the Latin West until the sixteenth century. The subject of Pliny's work is Nature--that is, life itself (pref. 13)--as seen by eyes thoroughly Roman and Stoic. Divine Nature herself provides all that humans need, and they ought to make proper use of Nature's providence--Pliny constantly condemns luxuria (luxury) as an abuse of Nature. Romans once read...