New Defender's Study Bible Notes
18:21 into the sea. See Jeremiah 51:41-42,63-64. This final disappearance of Babylon, possibly brought about by an aftershock of the great earthquake, may well result from a sudden fracturing or slippage of the earth’s crust, causing the entire region to drop down below sea level. This event may occur some weeks or months after the great disaster (a nuclear explosion or perhaps even fire from heaven) that left the great city in ashes. This would give time for the ancient prophecies of Babylon’s great desolation to be literally fulfilled (e.g., Isaiah 13:20-22; Jeremiah 51:62; Revelation 18:2).