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."

Revelation 18:2, "And he cried mightily with a strong voice, saying, Babylon the great is fallen, is fallen, and is become the habitation of devils, and the hold of every foul spirit, and a cage of every unclean and hateful bird."

Revelation 18:10, "Standing afar off for the fear of her torment, saying, Alas, alas, that great city Babylon, that mighty city! for in one hour is thy judgment come."

Revelation 18:21, "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."

It seems that Jerusalem having picked up new ideas from Babylon is stated here (Babylon having infiltrated Zion [the original Judaism]):

Zechariah 2:7-12, "Deliver thyself, O Zion, that dwellest with the daughter of Babylon. [...] Sing and rejoice, O daughter of Zion: for, lo, I come, and I will dwell in the midst of thee, saith the Lord. And many nations shall be joined to the Lord in that day, and shall be my people: and I will dwell in the midst of thee, and thou shalt know that the Lord of hosts hath sent me unto thee. And the Lord shall inherit Judah his portion in the holy land, and shall choose Jerusalem again."

Babylon in the end times is compared to the Chaldeans and Sodom and Gomorrah in

Isaiah 13:19-21, "And Babylon, the glory of kingdoms, the beauty of the Chaldees' excellency, shall be as when God overthrew Sodom and Gomorrah. It shall never be inhabited, neither shall it be dwelt in from generation to generation: neither shall the Arabian pitch tent there; neither shall the shepherds make their fold there. But wild beasts of the desert shall lie there; and their houses shall be full of doleful creatures; and owls shall dwell there, and satyrs shall dance there."

Chaldean is interesting here since the Chaldean cipher is often used in the occult, see Table 1, p. 233 and Table 7, p. 235.

"never be inhabited" could be because there will be a New Jerusalem.

Revelation 21:1-2, "And I saw a new heaven and a new earth: for the first heaven and the first earth were passed away; and there was no more sea. And I John saw the holy city, new Jerusalem, coming down from God out of heaven, prepared as a bride adorned for her husband."

Revelation 11:8, "And their dead bodies shall lie in the street of the great city, which spiritually is called Sodom and Egypt, where also our Lord was crucified."

Isaiah 14:2-4, "And the people shall take them, and bring them to their place: and the house of Israel [spiritual Israel, see Romans 11] shall possess them in the land of the Lord for servants and handmaids: and they shall take them captives, whose captives they were; and they shall rule over their oppressors. And it shall come to pass in the day that the Lord shall give thee rest from thy sorrow, and from thy fear, and from the hard bondage wherein thou wast made to serve, That thou shalt take up this proverb against the king of Babylon, and say, How hath the oppressor ceased! the golden city ceased!"

Babylon also being "the golden city".