Matthew Poole and continuators on Joshua 8:17

17 And there was not a man left in Ai, or Bethel , that went not out after Israel: and they left the city open, and pursued after Israel.

To wit, fit for war.

Which, being a neighbouring City, and incouraged by the former success, had sent some Forces to assist them; and now, upon notice sent to them of the flight of their common Enemies, or upon some other signal given, which might easily be done, having been appointed before-hand, as is usual in such Cases, all their men of War joyn with those of Ai in the pursuit.