And they assembled them: the same verb is used in verse 14. It is helpful to specify both the subject and the object of the verb, as Good News Translation has done.

Armageddon: this is the transliteration (in Greek) of the Hebrew harmegiddo “the hill of Megiddo.” The name itself does not appear in the Old Testament. The Plain of Megiddo in northern Palestine was the scene of some important battles in Israelite history (see Judges 5.19; 2 Kgs 23.29-30; 2 Chr 35.22). Armageddon is the most commonly used English form of the word; but New Revised Standard Version has “Harmagedon”; Revised English Bible “Harmageddon”; Translator’s New Testament “Har-Magedon.” Is called may also be rendered “they call in the Hebrew language” or “has the name Armageddon in Hebrew.”

Quoted with permission from Bratcher, Robert G. and Hatton, Howard A. A Handbook on The Revelation to John. (UBS Handbook Series). New York: UBS, 1993. For this and other handbooks for translators see here .