subject matter of each book. This has been shown in Heinrich Brunn's Disputatio (Bonn, 1856). One of Pliny's authorities is Marcus Terentius Varro. In the geographical books, Varro is supplemented by the topographical commentaries of Agrippa, which were completed by the emperor Augustus; for his zoology, he relies largely on Aristotle and on Juba, the scholarly Mauretanian king, studiorum claritate memorabilior quam regno (v. 16). Juba is one of his principal guides in botany; Theophrastus is also named in his Indices, and Pliny had translated Theophrastus's Greek into Latin. Another work by Theophrastus, On Stones was cited as a source on ores and minerals. Pliny strove to use all the Greek histories available to him, such as Herodotus and Thucydides, as well as the Bibliotheca Historica of Diodorus Siculus. Working method His nephew, Pliny the Younger, described the method that Pliny used to write the Natural History: Does it surprise you that a busy man found time to finish so many volumes, many of which deal with such minute details?... He used to begin to study at night on the Festival of Vulcan, not for luck but from his love of study, long before dawn; in winter he would commence at the seventh hour... He could sleep at call, and it would come upon him and leave him in the middle of his work. Before daybreak he would go to Vespasian – for he too was a night-worker – and then set about his official duties. On his return home he would again give to study any time that he had free. Often in summer after taking a meal, which with him, as in the old days, was always a simple and light one, he would lie in the sun if he had any time to spare, and a book would be read aloud, from which he would take notes and extracts. Pliny the Younger told the following anecdote illustrating his uncle's enthusiasm for study: After dinner a book would be read aloud, and he would take notes in a cursory way. I remember that one of his friends, when the reader pronounced a word wrongly, checked him and made him read it again, and my uncle said to him, "Did you not catch the meaning?" When his friend said "yes," he remarked, "Why then did you make him turn back? We have lost more than ten lines through your