In the 1st book, the author enters into a long discussion on the merits of Homer, whom he considers to have been the earliest geographer, and defends him against the errors and misconceptions of Eratosthenes. He corrects some faults of Eratosthenes, and, in his inquiry concerning the natural changes of the earth’s surface defends Eratosthenes against Hipparchus. In conclusion, he again corrects Eratosthenes as regards the magnitude and divisions of the inhabited world. The most remarkable passage in this book is that in which he conjectures the existence of the great Western Continents.[15] The 2nd book is chiefly occupied with some accounts of mathematical geography, and the Author defends against Hipparchus the division of the inhabited world adopted by Eratosthenes into sections. Then follows a criticism of the division of the earth into six zones, as taught by Poseidonius and Polybius. The pretended circumnavigation of Africa by Eudoxus is referred to, as well as some geographical errors of Polybius. He makes observations of his own on the form and size of the earth in general, as well as of the inhabited portion of it, describing the method of representing it on a spherical or plane surface. A short outline is given of seas, countries, and nations; and he concludes with remarks on the system of climates,[16] and on the shadows projected by the sun. The 3rd book commences with Iberia, and the subject of Europe is continued to the end of the 10th book. His references are the Periplus of Artemidorus, Polybius, and Poseidonius; all three of whom wrote as eye-witnesses. For descriptions and measurement of distances, Artemidorus is chiefly depended upon. The information possessed by Eratosthenes of these countries was meagre and uncertain. For the nations of southern Iberia, he adopts the account of Asclepiades of Myrlea, who had lived and been educated there. Some statements also are borrowed from Roman authors. The 4th book contains Gallia, according to the four divisions then existing, viz. Gallia Narbonensis, Acquitanensis, Lugdunensis, and the Belgæ; also Britain, with Ierne, and Thule; and lastly, the Alps. Here Eratosthenes and Ephorus are of little service. His chief guide is Julius Cæsar, whom he frequently quotes _verbatim_. Polybius is his guide for the Alps. Pytheas is the source of some scanty information respecting Ierne and Thule. Throughout his description he adds accounts obtained at Rome from travellers.