The Naturalis historia is the Encyclopedia of antiquity. The work is the result of the study, declared by Pliny himself, of 2000 volumes, most of which are lost to us, and is therefore the sole source of the events of large and small characters and of otherwise obscure or unknown historical anecdotes. The numerous references are intertwined with the material covered in the chapter, whether we talk about animals, geographical notations, medicines and poisons, architecture and statuary (the eagles of the legions, Mithridates, the triumphs etc.) The 37 books, which have come down to us almost complete, include the human knowledge of the classical era: - A description of the cosmos and the world, derived from the always surprising level of knowledge of the Greek and Eastern world. Notably, in addition to the simple demonstrations of the sphericity of the earth, the (rational) intuition of the attraction between the masses, of the distribution of temperate lands in ours and, even if Pliny could only imagine it, in the other hemisphere, and the consideration of the earth as "a point in the universe". The theological clarity is also surprising and ironic: “Almighty gods? Can they possibly change the past? Can they prevent me from living?” “They cannot make two times ten not twenty.” - The description of every type of matter and living being, with, among other things, accurate observations on animal behaviour, alternating with imaginative legends that Pliny suggests "not to accept without reservations" but which however, from time to time amused or irritated, reports: “Many other wonders are told about this animal, but above all that in the shepherds' stalls it counterfeits human speech and learns someone's name and, calling them out, tears them to pieces”. - The customs of the Romans, Greeks but also of the most remote populations of Asia and Africa. And where scientific rigour gives way to legend, the value of the work, rather than diminishing, is ennobled by the mythological and legendary contributions collected from every part of the known world: thus we will have "the Blemmis, headless and with mouth and eyes on the chest, the Sciapods, who have only one leg but are very fast in jumping, and when the heat of the sun is greater they lie down and protect themselves with the shadow of their feet". - The exploration of human activities, from agriculture to factories to philosophy, with the constant criticism of the Greeks, considered vainglorious and even a little liars; the warning, even derisively, against the magical activities that invade medicine; a ferocious moralism against the excesses of luxury: “Lucius Plotius, brother of Lucius Plancus, twice consul and censor, after being proscribed by the Triumvirs was betrayed in his hiding place in Salernum by the smell of his ointments, a misfortune which far surpassed all the guilt deriving from its proscription. Indeed, who can believe that men like these do not fully deserve a violent end?” - The history of the arts, painting and sculpture above all, with the description of works, materials and techniques, information that has often reached us only through Pliny. - The history of metals and precious stones, their origin and their connections with human and historical events. Therefore, pervading the entire work, a monumental amount of pharmacological information, fascinating even when evidently imaginative, but after all, natural medicine still today feeds on traditional uses looking at the effect, without investigating the mechanisms of action; the similia similibus curantur of ancient medicine, taken up by the modern "homeopathic" method, is also evident.