There are nevertheless indications that the Greeks had commercial relations with the coasts of the Baltic and North Sea, and fresh obscure statements, which may be derived from such a connection, appear later in Pliny, and to some extent also in Mela. It may be supposed that enterprising Greek traders and seamen, enticed by Pytheas's accounts of the amber country, attempted to follow in his track, and succeeded in reaching the land of promise whence this costly commodity came. And if they had once found out the way, they would certainly not have relinquished it except upon compulsion. But it must be remembered that the voyage was long, and that they had first to pass through the western Mediterranean and the Pillars of Hercules, where the Carthaginians had regained their power and obtained the command of the sea. The overland route was easier and safer; it ran through the country of tribes which in those distant times may have been comparatively peaceful. The trade communication between the Black Sea and the Baltic countries seems, as mentioned above, to have developed early, and it may be thought that the active Greek traders would try it in order to reach a district where so much profit was to be expected; but no certain indication of this communication can be produced from any older author of note after Pytheas's time, so far as we know them, and even so late an author as Ptolemy has little to tell us of the regions east of the Vistula.
The founder of scientific geography, Eratosthenes (275-circa 194 B.C.),[73] librarian of the Museum of Alexandria, based what he says of the North chiefly on Pytheas. He divided the surface of the earth into climates (zones) and constructed the first map of the world, whereon an attempt was made to fix the position of the various places by lines of latitude and meridians. He started with seven known points, along the old meridian of Rhodes. They were: Thule, the Borysthenes, the Hellespont, Rhodes, Alexandria, Syene, and Meroe. Through these points he laid down lines of latitude (see the map). He also made an attempt to calculate the circumference of the globe by measurement, and found it 250,000 stadia (== 25,000 geographical miles), which is 34,000 stadia (== 3400 geographical miles) too much. He placed the island of Thule under the Arctic Circle,[74] far out in the sea to the north of Brettanice. This was to him the uttermost land and the northern limit of the "œcumene," which he calculated to be 38,000 stadia (== 3800 geographical miles) broad,[75] which according to his measurement of the circumference of the earth is about 54° 17', since each of his degrees of latitude will be about 700 stadia. His "œcumene" thus extended from the latitude of the Cinnamon Coast (Somaliland) and Taprobane (Ceylon), 8800 stadia north of the equator, to the Arctic Circle. South of it was uninhabitable on account of the heat, and north of it all was frozen.