the throne of the beast: John might be referring to Rome, the political power of his time. Built on seven hills (Revelation 17:9), Rome's empire stretched across the sea (13:1) and dominated the world (13:7).
plunged into darkness: This is similar to the ninth plague of Egypt (Exodus 10:22) and the fourth trumpet (Revelation 8:12).
gnaw their tongues. … curse the God of heaven: Pain and anger caused these reactions to punishment (compare Matthew 8:12; 13:42, 50; 22:13; 24:51; 25:30; Luke 13:28).