Revelation 18:17

The last sort of mourners for Babylon's ruin are sailors and seamen; all spiritual seamen that have an oar in St. Peter's boat shall lament greatly, whose life and livelihood did depend upon the merchant trade of that great city; these, though they stuck close to her, and trafficked with her in the day of her prosperity, yet now with the rest they stand afar off from her, lamenting her ruin, and their own loss, in the day when her desolation cometh.

And, as an evidence of the greatness of their sorrow and mourning, they are here said to cast dust on their heads; which amongst the ancients was used as. special token of extraordinary grief and sorrow, Job 2:13. In. time of deep affliction we may express our outward sorrows by our outward gestures: those mourners for Babylon express their sorrow for her and themselves, by casting dust upon their heads.