Aerial from north
The site of et-Tell is a prominent ruin that is usually identified as biblical Ai. Archaeological excavations though have shown that et-Tell was inhabited from 3000-2400 B.C. and again after 1200 B.C., but not during the time of Joshua's Conquest (1400 B.C.). Resorting to a "late date" theory of the Conquest does not solve the problem.
Read more at http://www.bibleplaces.com/ettell.htm