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.