Howl, ye ships of Tarshish (comp. Isaiah 23:1). The ships that traded with Tarshish, not those belonging to Tarshish, are intended. Your strength is laid waste; rather, your stronghold; i.e. Tyre itself.
The elegy ends as it began, with a statement of the bare fact. Alexander's destruction of the city was the final and complete fulfillment of the prophecy. The captures by Esarhaddou, by Asshur-bani-pal, and by Nebuchadnezzar, were anticipations of the final one, and partial fulfillments of the prophecy.