What is Babylon in Revelation?
Already before Revelation, Babylon is mentioned by Peter:
1 Peter 5:13, "The church that is at Babylon, elected together with you, saluteth you; and so doth Marcus my son."
Wikipedia says that Peter therefore must have written from Rome. Let's see what the King James Version (KJV) of the Bible says.
Revelation 14:8, "And there followed another angel, saying, Babylon is fallen, is fallen, that great city, because she made all nations drink of the wine of the wrath of her fornication."
Revelation 16:19, "And the great city was divided into three parts, and the cities of the nations fell: and great Babylon came in remembrance before God, to give unto her the cup of the wine of the fierceness of his wrath."