Oecumenius

And they went up over the extent of the earth, and they will surround the camp of the saints and the beloved city. And fire came down from God out of heaven and devoured them. And they will surround the beloved city, that is, the Church. But fire brought from heaven will devour them all, and when the end has come, the prime evil Satan will be cast together with the Devil and the Antichrist into the lake of fire, that is, Gehenna.

Commentary on Revelation ↗

Augustine of Hippo

[That they encompassed the beloved city] obviously does not mean that they gathered or will gather in some one place where, we must suppose, the camp of the saints and the beloved city is to be. For, of course, this city is Christ's church, which is spread over the whole world. Wherever his church will be (and it will be among all nations, "over the breadth of the earth"), there is to be the camp of the saints and the beloved city of God. …

City of God 20.11-12 ↗

Bede

And fire came down from God out of heaven and devoured them. This should not be considered the final punishment, but rather the fire of envy by which they will be tormented, the adversity stemming from the firmness of the saints. For heaven is the firmament. This is the fire that came out of the mouth of God's witnesses and devours their enemies. For on the last day, fire will not rain upon them, but the gathered and judged will be cast into the eternal fire, of which it is also said here:

Commentary on Revelation ↗

Victorinus of Pettau

"And they went up upon the breadth of the earth, and compassed the camp of the saints about, and the beloved city; and fire came down from God out of heaven, and devoured them. And the devil who seduced them was cast into the take of fire and brimstone, where both the beast and the false prophet shall be tormented day and night for ever and ever."]This belongs to the last judgment. …

Commentary on the Apocalypse of the Blessed John ↗