Strabo Geography 11.2.2

[2] The Tanaïs or Don flows from the northern parts. It does not however flow in a direction diametrically opposite to the Nile, as some suppose, but its course is more to the east than that of the latter river; its sources, like those of the Nile, are unknown. A great part of the course of the Nile is apparent, for it traverses a country the whole of which is easy of access, and its stream is navigable to a great distance from its mouth. We are acquainted with the mouths of the Don, (there are two in the most northerly parts of the Maeotis, distant 60 stadia from each other,) but a small part only of the tract above the mouths is explored, on account of the severity of the cold, and the destitute state of the country; the natives are able to endure it, who subsist, like the wandering shepherd tribes, on the flesh of their animals and on milk, but strangers cannot bear the climate nor its privations. Besides, the nomades dislike intercourse with other people, and being a strong and numerous tribe have excluded travellers from every part of the country which is accessible, and from all such rivers as are navigable. For this reason some have supposed that the sources of the river are among the Caucasian mountains, that, after flowing in a full stream towards the north, it then makes a bend, and discharges itself into the Maeotis. Theophanes ¹ of Mitylene is of the same opinion with these writers. Others suppose that it comes from the higher parts of the Danube, but they do not produce any proof of so remote a source, and in other climates, though they seem to think it impossible for it to rise at no great distance and in the north.