Strabo Geography 2.1.3

[3] But there is another method (says Eratosthenes) of proving this. The distance from the Gulf of Issus to the Euxine, proceeding in a northerly direction towards Amisus ¹ and Sinope, ² is about 3000 stadia, which is as much as the supposed extent of the mountains [of the Taurus]. ³ The traveller who directs his course from Amisus due east, ⁴ arrives first at Colchis, then at the high lands by the Hyrcanian Sea, ⁵ afterwards at the road leading to Bactra, ⁶ and beyond to the Scythians; having the mountains always on the right. The same line drawn through Amisus westward, crosses the Propontis and Hellespont. From Meroe to the Hellespont there are not more than 18,000 stadia. ⁷ The distance is just the same from the southern extremity of India to the land of Bactria, if we add to the 15,000 stadia of that country the 3000 which its mountains occupy in breadth.