Joshua sent men from Jericho to Ai, which is beside Beth Aven, on the east side of Bethel, and spoke to them, saying, Go up and spy out the land. The men went up and spied out Ai.
(2) Joshua was written so long after the events recorded (by imposters, of course) that they included errors in their book.  This alleged solution is unchristian and absolutely impossible for believers to accept.