Previously in Herodotus
49. These are the native Scythian rivers which join to swell its stream, while from the Agathyrsians flows the Maris and joins the Ister, and from the summits of Haimos flow three other great rivers towards the North Wind and fall into it, namely Atlas and Auras and Tibisis. Through Thrace and the Thracian Crobyzians flow the rivers Athrys and Noes and Artanes, running into the Ister; and from the Paionians and Mount Rhodope the river Kios, cutting through Haimos in the midst, runs into it also. From the Illyrians the river Angros flows Northwards and runs out into the Triballian plain and into the river Brongos, and the Brongos flows into the Ister; thus the Ister receives both these, being great rivers. From the region which is above the Ombricans, the river Carpis and another river, the Alpis, flow also towards the North Wind and run into it; for the Ister flows in fact through the whole of Europe, beginning in the land of the Keltoi, who after the Kynesians dwell furthest towards the sun-setting of all the peoples of Europe; and thus flowing through all Europe it falls into the sea by the side of Scythia.
50. So then it is because these which have been named and many others join their waters together, that Ister becomes the greatest of rivers; since if we compare the single streams, the Nile is superior in volume of water; for into this no river or spring flows, to contribute to its volume. And the Ister flows at an equal level always both in summer and in winter for some such cause as this, as I suppose:—in winter it is of the natural size, or becomes only a little larger than its nature, seeing that this land receives very little rain in winter, but constantly has snow; whereas in summer the snow which fell in the winter, in quantity abundant, melts and runs from all parts into the Ister. This snow of which I speak, running into the river helps to swell its volume, and with it also many and violent showers of rain, for it rains during the summer: and thus the waters which mingle with the Ister are more copious in summer than they are in winter by about as much as the water which the Sun draws to himself in summer exceeds that which he draws in winter; and by the setting of these things against one another there is produced a balance; so that the river is seen to be of equal volume always.
51. One, I say, of the rivers which the Scythians have is the Ister; and after it the Tyras, which starts from the North and begins its course from a large lake which is the boundary between the land of the Scythians and that of the Neuroi. At its mouth are settled those Hellenes who are called Tyritai.
52. The third river is the Hypanis, which starts from Scythia and flows from a great lake round which feed white wild horses; and this lake is rightly called Mother of Hypanis. From this then the river Hypanis takes its rise and for a distance of five days' sail it flows shallow and with sweet water still; but from this point on towards the sea for four days' sail it is very bitter, for there flows into it the water of a bitter spring, which is so exceedingly bitter that, small as it is, it changes the water of the Hypanis by mingling with it, though that is a river to which few are equal in greatness. This spring is on the border between the lands of the agricultural Scythians and of the Alazonians, and the name of the spring and of the place from which it flows is in Scythian Exampaios, and in the Hellenic tongue Hierai Hodoi. Now the Tyras and the Hypanis approach one another in their windings in the land of the Alazonians, but after this each turns off and widens the space between them as they flow.
53. Fourth is the river Borysthenes, which is both the largest of these after the Ister, and also in our opinion the most serviceable not only of the Scythian rivers but also of all the rivers of the world besides, excepting only the Nile of Egypt, for to this it is not possible to compare any other river: of the rest however the Borysthenes is the most serviceable, seeing that it provides both pastures which are the fairest and the richest for cattle, and fish which are better by far and more numerous than those of any other river, and also it is the sweetest water to drink, and flows with clear stream, though others beside it are turbid, and along its banks crops are produced better than elsewhere, while in parts where it is not sown, grass grows deeper. Moreover at its mouth salt forms of itself in abundance, and it produces also huge fish without spines, which they call antacaioi, to be used for salting, and many other things also worthy of wonder. Now as far as the region of the Gerrians, to which it is a voyage of forty days, the Borysthenes is known as flowing from the North Wind; but above this none can tell through what nations it flows: it is certain however that it runs through desert to the land of the agricultural Scythians; for these Scythians dwell along its banks for a distance of ten days' sail. Of this river alone and of the Nile I cannot tell where the sources are, nor, I think, can any of the Hellenes. When the Borysthenes comes near the sea in its course, the Hypanis mingles with it, running out into the same marsh; and the space between these two rivers, which is as it were a beak of land, is called the point of Hippoles, and in it is placed a temple of the Mother, and opposite the temple upon the river Hypanis are settled the Borysthenites.
- Herodotus, Book IV
More Information: from the New Yorker Magazine, Herodotus's Book.