The apostle John recognizes that judgment is being made against Babylon when he sees the strong angel toss a stone like a great
millstone (Rev 18:21).
Two heavy circular millstones are used for grinding grain: one lying flat as a base and the other standing up
rolling on an axel atop of the flat circular base.
Then a strong angel took up a stone like a great millstone and threw it into the sea, saying, "So
will Babylon, the great city, be thrown down with violence, and will not be found any longer."
(Rev 18:21)
When speaking of deceit and causing others to go astray, Jesus mentions the use of a millstone in the figurative
sense to warn against and emphasize the seriousness of the offense. And this is what Babylon was precisely guilty of.
Whoever causes one of these little ones who believe to stumble, it would be better for him if, with a heavy
millstone hung around his neck, he had been cast into the sea. (Mark 9:42)