isaiah 23:15 And it shall come to pass in that day, that Tyre shall be forgotten seventy years, according to the days of one king: after the end of seventy years shall Tyre sing as an harlot. - Free Bible Online

      15. forgotten--Having lost its former renown, Tyre shall be in obscurity.
      seventy years--(so Jer 25:11, 12; 29:10).
      days of one king--that is, a dynasty. The Babylonian monarchy lasted properly but seventy years. From the first year of Nebuchadnezzar to the taking of Babylon, by Cyrus, was seventy years; then the subjected nations would be restored to liberty. Tyre was taken in the middle of that period, but it is classed in common with the rest, some conquered sooner and others later, all, however, alike to be delivered at the end of the period. So "king" is used for dynasty (Da 7:17; 8:20): Nebuchadnezzar, his son Evil-merodach, and his grandson, Belshazzar, formed the whole dynasty (Jer 25:11, 12; 27:7; 29:10).
      shall Tyre sing as . . . harlot--It shall be to Tyre as the song of the harlot, namely, a harlot that has been forgotten, but who attracts notice again by her song. Large marts of commerce are often compared to harlots seeking many lovers, that is, they court merchants of all nations, and admit any one for the sake of gain (Na 3:4; Re 18:3). Covetousness is closely akin to idolatry and licentiousness, as the connection (Eph 5:5; Col 3:5) proves (compare Isa 2:6-8, 16).

JFB.