Millstones

And a mighty angel took up a stone like a great millstone, and cast it into the sea, saying, Thus with violence shall that great city Babylon be thrown down, and shall be found no more at all. Revelation 18:21

The size of a great millstone. The name "Gat-Sh’manim" ("Gethsemane," Mt 26:36&N) means "oil press," that is, a stone mill for grinding olives into pulp for their oil. Until quite recently the Arabs in the villages here in Israel used such presses for the same purpose, and many of the millstones are sill around. They are circular with a hole in the center about 9 inches square; diameter averages about five feet, thickness a foot and their weight well over a ton.

(Stern, David H. 1996. Jewish New Testament Commentary. Clarksville, MD: Jewish New Testament Publications., pg 837)