 The passageways through each of the gates are 20 metres ( 66 ft ) long , and have vaulted ceilings with hidden machicolation openings in their ceilings . The lower part of each tower is of solid stone , while the upper third has a vaulted room with arrowslits . An unusual feature of the wall near Bab al @-@ Nasr is a stone latrine which appears like a balcony . The wall between Bab al @-@ Nasr and Bab al @-@ Futuh contains an inscription of Quranic texts in Kufic characters . 
