John Calvin Commentary Joshua 8:25

"And all that fell that day, both of men and women, were twelve thousand, even all the men of Ai." — Joshua 8:25 (ASV)

And so it was that all that fell that day, etc. The meaning is not that all the killed were inhabitants of Ai, but that all who lived in it were killed, so that not one escaped. It has already been seen that the inhabitants of Bethel were mixed in with them; and as no mention of that city is made afterwards, it may be conjectured with some probability that they had abandoned their own town, which was not well fortified, and had taken refuge for greater safety in one which they hoped could be easily defended.

The words, therefore, simply mean that all who had come out of the city and all who were found in it were killed to the last man. If any are more inclined to think that this number of those whose killing took place within the walls is confined to the aged, the sick, the women, and the children, I will not dispute the matter. Still, if we consider that only a small town was joined with a city that was not very large or populous, it is more probable that the number also includes those who fell in battle.