Albert Barnes Commentary Revelation 18:21

"And a strong angel took up a stone as it were a great millstone and cast it into the sea, saying, Thus with a mighty fall shall Babylon, the great city, be cast down, and shall be found no more at all." — Revelation 18:21 (ASV)

And a mighty angel. (See Barnes' commentary on Revelation 18:1).

This seems, however, to have been a different angel from the one mentioned in Revelation 18:1, though, like that one, he is described as having great power.

Took up a stone like a great millstone. (On the structure of mills among the ancients, see Barnes' commentary on Matthew 24:41).

And cast it into the sea. This served as an emblem of the utter ruin of the city, indicating that the city would be as completely destroyed as that stone was covered by the waters.

Saying, Thus with violence. This means with force—just as the stone was thrown into the sea.

The idea is that its destruction would not occur through a gentle and natural decline, but by the application of foreign power.

This accords with all the representations in this book that violence will be employed to overthrow the Papal power .

The origin of this image is probably Jeremiah 51:63-64: And it shall be, when thou hast made an end of reading this book, that thou shalt bind a stone to it, and cast it into the midst of Euphrates; and thou shalt say, Thus shall Babylon sink, and shall not rise from the evil that I will bring on her.