Joshua 8:12 - Ellicott's Commentary On The Whole Bible

And he took about five thousand men, and set them to lie in ambush... — Is this a fresh body, or only a portion of the thirty thousand mentioned in Joshua 8:3? It is, of course, possible that the body of thirty thousand, having closed the communications between Bethel and Ai on the first night, and finding that they were more numerous than was necessary, had rejoined Joshua when he came up, and that a small body of five thousand was told off for the service on the next day. But after carefully studying the natural features of the position by the Ordnance map (of which I have been able to enjoy the advantage at this point of my work), I am inclined to think that both forces were employed — the thirty thousand and the five thousand — and for distinct services. There are two ravines, which come to a head between Beitin (Bethel) and et-Tel (Ai). The body of men who were to fire the town of Ai were posted in the one nearer to Ai. The larger body, whose business was to prevent any interference from the side of Bethel, were posted in the ravine next to that city, where they had been from the first. If it be remembered, as was before observed, that Joshua was attacking a fortified town, which was protected in flank by another town, and that it was necessary to be prepared for all contingencies from the first, the meaning of his movements will be apparent.