Charles Ellicott Commentary Judges 20:40

"But when the cloud began to arise up out of the city in a pillar of smoke, the Benjamites looked behind them; and, behold, the whole of the city went up [in smoke] to heaven." — Judges 20:40 (ASV)

When the flame began to arise up. —Rather, when the column (of smoke), as in Judges 20:38.

The flame of the city. —Literally, the whole of the city —i.e., the universal conflagration—a very powerful expression. (Septuagint, συντέλεια τῆς πόλεως.)