Poshtab Castle is one of the most important and valuable historical monuments of Ahar which is located on a 3000 meters high mountain. The only access to this castle is by the 220 stony steps. Objects obtained from the castle indicate that this castle built in the early dominance of Islam to Arasbaran and Ghare Dag. From these castles like Babak castle perhaps simultaneously battle with Arabs rulings to the region has been used military.