The morning after the defeat at Ai,Joshua gathered all the Israelites before the lord.god revealed that it was achan. Achan then confessed that he has stolen some things from Jericho and had hid them under his tent. Joshua took the things achan stole,and took achan,his family,and his livestock to the valley of achor,where he stoned them to death and burnt them,it may seem that the punishment was severe,but it shows clearly that the sin of achan was great.