Albert Barnes on Revelation 18:19

And they east dust on their heads. A common sign of lamentation and mourning among the Orientals. Job 2:12.

By reason of her costliness. The word rendered costliness-- τιμιοτης--means, properly, preciousness, costliness; then magnificence, costly merchandise. The luxury of a great city enriches many individuals, however much it may impoverish itself.

For in one hour is she made desolate. So it seemed to them. Rev 18:17.

(d) "cast dust" Josh 7:6, Job 2:12, Eze 27:30