A.T. Robertson Commentary Revelation 18:2

"And he cried with a mighty voice, saying, Fallen, fallen is Babylon the great, and is become a habitation of demons, and a hold of every unclean spirit, and a hold of every unclean and hateful bird." — Revelation 18:2 (ASV)

Fallen, fallen is Babylon the great (επεσεν, επεσεν Βαβυλων η μεγαλη). The very words of 14:8: "Did fall, did fall Babylon the great." Prophetic aorists of πιπτω repeated like a solemn dirge of the damned.

Is become (εγενετο). Prophetic aorist middle.

A habitation of devils (κατοικητηριον). Late word (from κατοικεω, to dwell), in N.T. only here and Eph 2:22. Devils should be demons, of course. So Isaiah prophesied of Babylon (Isaiah 12:21f.) and also Jeremiah (Jeremiah 50:39) and Zephaniah of Nineveh (Zephaniah 2:14). Both Babylon and Nineveh are ruins.

A hold of every unclean spirit (φυλακη παντος πνευματος ακαθαρτου). Φυλακη is garrison or watch-tower as in Hab 2:1, rather than a prison (20:7).

A hold of every unclean and hateful bird (φυλακη παντος ορνεου ακαθαρτου κα μεμισημενου). Ορνεου is old word for bird, in N.T. only Re 18:2; 19:17,21. "The evil spirits, watching over fallen Rome like night-birds or harpies that wait for their prey, build their eyries in the broken towers which rise from the ashes of the city" (Swete). Long ago true of Babylon and Nineveh, some day to be true of Rome.