History reveals the great city of Babylon was conquered in one night, without resistance, in 539 BC by Cyrus the Great. Revelation 14:8 reads:
14:8 And there followed another Angel, saying, Babylon is fallen, is fallen, that great citie, because she made all nations drink of the wine of the wrath of her fornication.
That must be the wall scholars refer to. Twelve feet deep surrounding the city. About three hundred years later, Alexander took Babylon for Greece and all those rocks became a quarry for Greek new construction. How's that for an insult!