Destruction of Ai 

God commands Joshua to stretch out his spear toward the city of Ai (verse 18). Not only was this a signal to begin the attack (verse 19), but it was also a symbol of God's presence and help to His people in the battle (compare verses 1, 18)—displayed in the fact that Joshua did not lower his spear until the victory was won (verse 26). This is powerfully reminiscent of Israel's first battle upon leaving Egypt against the Amalekites, where Moses held aloft the rod of God, which was also a symbol of God's participation in the battle (Exodus 17:8-16). Remarkably, Joshua had been the military commander in that former battle, looking to Moses with the rod. Now here he was with raised spear, standing as the one others were looking to. Of course, it was recognized in both instances that God was the one directing the outcome.

Along with the defeat of Ai, the city of Bethel is also mentioned (verse 17). "Bethel was near Ai to the west (Joshua 7:2), although its exact site is disputed. The inhabitants of Bethel came out of their city to help the men of Ai. Since the Israelite ambush was stationed between Bethel and Ai [Joshua 8:12], they may have felt threatened by the Israelites. Or it may be that Ai was a small outpost for the larger city of Bethel (Joshua 7:3) and an attack on Ai was understood to be an attack on Bethel. The text does not record Bethel's defeat, although its king is listed among those conquered by Joshua (Joshua 12:16). It may be that in the defeat of Ai, Bethel was also defeated and no further reference was needed" (Nelson Study Bible, note on Joshua 8:17).

Following the Israelites' defeat of Ai, Joshua led them to Shechem, which is between Mount Ebal and Mount Gerizim, near modern-day Nablus. There he carried out the commands of God and Moses to build an altar, erect massive stones engraved with the Book of the Law, review the law, and rehearse the blessings and curses (verses 30-35; compare Deuteronomy 11:29-32; Deuteronomy 27:1-26). Afterward, they apparently returned to Gilgal, where they first camped after crossing the Jordan (compare Joshua 9:6).

Supplementary Reading: "A Good News Interview With Bryant Wood, Ph.D.: The Bible vs. Modern Scholarship," The Good News, March-April 2002, pp. 12-13.