They threw dust on their heads: a sign of grief (see Ezek 27.30). So one may translate “They threw dust on their heads to show their grief (or, how sorry they were).”

Wept and mourned: as in verses 11 and 15.

Alas, alas for the great city: as in verses 10 and 16.

Where all who had ships at sea grew rich by her wealth: “all seafaring traders became rich from her wealth (or, prosperity)” or “all shipowners who travel on the sea to buy and sell gained many possessions from Babylon’s wealth.” The Greek word translated wealth is the superlative form of the adjective “valuable” (see its use in verse 12, “costly wood”), and appears only here in the New Testament.

In one hour she has been laid waste: see the similar expression in verse 17.

Quoted with permission from Bratcher, Robert G. and Hatton, Howard A. A Handbook on The Revelation to John. (UBS Handbook Series). New York: UBS, 1993. For this and other handbooks for translators see here .