[Sidenote: Dionysius Periegetes, 117-138 A.D.]
The so-called Dionysius Periegetes wrote in the time of the emperor Hadrian (117-138 A.D.) a description of the earth in 1187 verses, which perhaps on account of its simple brevity and metrical form was used in schools and widely circulated [cf. K. Miller, vi., 1898, p. 95]. But unfortunately the author has merely drawn from obsolete Greek sources, such as Homer, Hecatæus, Eratosthenes and others, and has nothing new to tell us. The whole continent was surrounded by ocean like an immense island; it was not quite circular, but somewhat prolonged in the direction of the sun's course (i.e., towards the east and west).
After Greek scientific geography had had its most fruitful life in the period ending with Eratosthenes and Hipparchus it still sent out such powerful shoots as the physical-mathematical geographer Posidonius and the descriptive geographer Strabo; but after them a century and a half elapses until we hear of its final brilliant revival in Marinus of Tyre and Claudius Ptolemy, whose work was to exercise a decisive influence upon geography thirteen centuries later.
Marinus's writings are lost, and we know nothing more of him than is told us by his younger contemporary Ptolemy, who has relied upon him to a considerable extent, and whose great forerunner he was. He must have lived in the first half of the second century A.D. He made an exhaustive attempt to describe every place on the earth according to its latitude and longitude, and drew a map of the world on this principle. He also adopted Posidonius's insufficient estimate of the earth's circumference (instead of that of Eratosthenes), and his exaggerated extension of the "œcumene" towards the east; and as this was passed on from him to Ptolemy he exercised great influence upon Columbus, amongst others, who thus came to estimate the distance around the globe to India at only half its real length. In this way Marinus and Ptolemy are of importance in the discovery not only of the West Indies, but also of North America by Cabot, and in the earliest attempts to find a north-west passage to China. Thus "accidental" mistakes may have far-reaching influence in history.