Ai - (Easton's Bible Dictionary)
Ruins. (1.) One of the royal cities of the Canaanites (Josh. 10:1; Gen. 12:8; 13:3). It was the scene of Joshua's defeat, and afterwards of his victory. It was the second Canaanite city taken by Israel (Josh. 7:2-5; 8:1-29). It lay rebuilt and inhibited by the Benjamites (Ezra 2:28; Neh. 7:32; 11:31). It lay to the east of Bethel, "beside Beth-aven." The spot which is most probably the site of this ancient city is Haiyan, 2 miles east from Bethel. It lay up the Wady Suweinit, a steep, rugged valley, extending from the Jordan valley to Bethel.
(2.) A city in the Ammonite territory (Jer. 49:3). Some have thought that the proper reading of the word is Ar (Isa. 15:1).