It was not till the sixth century B.C. that geography was recognized by the Greeks as a distinct branch of study. But Strabo was right in regarding Homer as the first Greek geographer, inasmuch as the Homeric poems provide the earliest literary evidence about the content of the Greek world. From Homer onwards the known world was continually enlarging its boundaries, and by the end of the Roman period very little, except the New World discovered by Columbus and his contemporaries, remained unknown. The progress of geographical knowledge may be divided into four stages—Homeric, Ionian, Hellenistic, Roman–in each of which the acquisition of data led on to an attempt at systematization, when the information provided by travellers was used as material for scientific theory. This process was unconscious in the Homeric stage, but deliberate in the others. Thus in the Ionian age the spread of colonization enabled Anaximander to make the first map and Hecataeus to write his Περίολος Γη~ς, the first systematic account of the world; these in their turn produced Herodotus, who brought to geography and ethnography the rudiments of a critical standpoint ( , vii. 152). In the Hellenistic and Roman ages the factors were not so much colonial as military and mercantile. Hellenistic knowledge of the world was enlarged by the campaigns of Alexander and by the enterprises of Alexandrian traders, which the scholars of Alexandria, notably Eratosthenes, the first truly critical geographer, turned to scientific use: similarly the progress of the Roman arms and the expansion of Roman trade brought grist to the mill of Strabo and Ptolemy, the most careful, respectively, of descriptive and scientific geographers. In the period which follows these, no longer ancient but medieval, the wheel comes full circle in a new Homeric stage of feudalism and fable, and starts its revolution once more; the next stage, the renascence Age of Discovery, is Ionia again on a larger scale.