Revelation 18:19

And they cast dust on their heads
As the seafaring men on account of Tyre, ( Ezekiel 27:30 ) this was a gesture used in mourning when persons were in afflicted and distressed circumstances, denoting disorder, confusion, and debasement; see ( Joshua 7:6 ) ( Job 2:12 )

and cried, weeping and wailing, saying, alas, alas! that great city;
as in ( Revelation 18:10 Revelation 18:16 ) so it was once, though now in flames:

wherein were made rich all that had ships in the sea;
not only the merchants of the earth, as in ( Revelation 18:3 ) the cardinals, archbishops, and bishops, but the governors of religious houses; these accumulated great wealth to themselves, and got the best of lands into their possession for the use and support of their abbeys and monasteries:

by reason of her costliness;
or costly things; pardons, indulgences, absolution, saying Mass, and praying souls out of purgatory, all which are costly, and hereby these traders have been enriched; and now the remembrance of these things, of which they will be deprived, will affect and grieve them, as well as the suddenness of Rome's ruin:

for in one hour is she made desolate;
her judgment come, and her riches come to nought, ( Revelation 18:10 Revelation 18:17 ) .