Joshua 8:20-21

20 The men of Ai looked back and saw the smoke of the city rising up into the sky, but they had no chance to escape in any direction; the Israelites who had been fleeing toward the wilderness had turned back against their pursuers.
21 For when Joshua and all Israel saw that the ambush had taken the city and that smoke was going up from it, they turned around and attacked the men of Ai.

Joshua 8:20-21 Meaning and Commentary

INTRODUCTION TO JOSHUA 8

Joshua is encouraged to go up and take Ai, and is directed what method to make use of, Jos 8:1,2; accordingly he set an ambush on the west side of it, and, he and the rest of the army went up before it, Jos 8:3-13; which, when the king of Ai saw, he and all his forces came cut against them, and the Israelites making a feint as if they were beaten, drew on the men of Ai to pursue them, upon which the ambush arose and entered the city and set fire to it, Jos 8:14-19; the smoke of which being observed by Joshua and Israel, they turned back upon the pursuers, and the ambush sallying out of the city behind them, made an entire destruction of them, then slew all the inhabitants, took the spoil, burnt the city, and hanged the king of it, Jos 8:20-29; after this Joshua built an altar at Ebal, wrote the law on stones, and read the blessings and curses in it before all Israel, Jos 8:30-35.

Cross References 2

Scripture quoted by permission.  Quotations designated (NIV) are from THE HOLY BIBLE: NEW INTERNATIONAL VERSION®.  NIV®.  Copyright © 1973, 1978, 1984, 2011 by Biblica.  All rights reserved worldwide.