Strabo Geography 7.3.15

[15] Near the outlets of the Ister River is a great island called Peuce; ¹ and when the Bastarnians took possession of it they received the appellation of Peucini. There are still other islands which are much smaller; some of these are farther inland than Peuce, while others are near the sea, for the river has seven mouths. The largest of these mouths is what is called the Sacred Mouth, ² on which one can sail inland a hundred and twenty stadia to Peuce. It was at the lower part of Peuce that Dareius made his pontoon-bridge, ³ although the bridge could have been constructed at the upper part also. The Sacred Mouth is the first mouth on the left as one sails ⁴ into the Pontus; the others come in order thereafter as one sails along the coast towards the Tyras; and the distance from it to the seventh mouth is about three hundred stadia. Accordingly, small islands are formed between the mouths. Now the three mouths that come next in order after the Sacred Mouth are small, but the remaining mouths are much smaller than it, but larger than any one of the three. According to Ephorus, however, the Ister has only five months. Thence to the Tyras, a navigable river, the distance is nine hundred stadia. And in the interval are two large lakes one of them opening into the sea, so that it can also be used as a harbor, but the other mouthless.

[15] Near the mouths of the Danube is the large island called Peuce. ¹ This the Bastarnae possessed, and were hence called Peucini. There are also other islands much smaller, some above this, and others nearer the sea. The Danube has seven mouths, the largest is called the Sacred Mouth, ² the passage by which to Peuce is 120 stadia. ³ At the lower part of this island Darius made his bridge. It might likewise have been constructed at the upper part. This is the first mouth on the left-hand side as you sail into the Black Sea; the rest are passed while sailing along towards the Dniester; the seventh mouth is distant from this first mouth about 300 stadia. These mouths form several islands. The first three mouths next after the Sacred Mouth are but small, the remainder are much less than it, but greater than any of the three. Ephorus states that the Danube has five mouths. From hence to the Dniester, ⁴ which is a navigable river, there are 900 stadia. ⁵ In the district intervening there are two great lakes; one is open to the sea, and is used as a harbour, ⁶ the other has no outlet.