Isaiah 23:15

seventy years The period fixed by Jeremiah for the duration of the Exile and the dominion of the Chaldæan Empire (ch. Isaiah 25:11 f., Isaiah 29:10). The number occurs frequently in the later literature: Zechariah 1:12; Zechariah 7:5; Daniel 9:2 ff.; 2 Chronicles 36:21. It is to be noted that in all these cases there is a reference more or less explicit to Jeremiah's prediction; and the use of the number here is probably to be accounted for in the same way. Ezekiel had used the number "forty" in a precisely similar manner (ch. Isaiah 4:6; Isaiah 29:13).

according to the days of one king The meaning is uncertain. Possibly it denotes a fixed, unalterable order of things, such as is maintained by the even rule of a single monarch. Some take it to mean "during the existence of one dynasty."

shall Tyre sing as a harlot Rather: it shall happen to Tyre according to the song of the harlot, evidently a well-known popular ballad, quoted in the next verse.