They gathered (συνηγαγεν). Second aorist active indicative of συναγω, singular (the three unclean spirits), like εκπορευετα in verse Revelation 16:14.

Har-Magedon (Hαρ-Μαγεδων). John proceeds now after the interruption in verse Revelation 16:15. Perhaps "the mountains of Megiddo" though not certain. Megiddo is in the valley of Esdraelon, and by the waters of Megiddo (the Kishon) Israel gained a decisive victory over Sisera (Judges 5:19), celebrated in Deborah's song. See also Revelation 20:8; Revelation 20:4.