The Mosque has several domes, the largest being over the mihrab and the entrance to the prayer hall from the courtyard. The dome of the mihrab is based on an octagonal drum with slightly concave sides, raised on a square base, decorated on each of its three southern, Easter and western faces with five flat-bottomed niches surmounted by five semi-circular arches, the niche in the middle is cut by a lobed oculus enrolled in a circular frame. This dome, whose construction goes back to the first half of the ninth century (towards 836), is one of the oldest and most remarkable domes in the western Islamic world.