Mizan or Shapour Dam is a relic of Sassanide era and divides the Karoon River into western and eastern sections. This dam is semi-circular in shape with two diverting arms or prolongations which deviates a part of the Karoon water to flow along the eastern region known as the Gerger river, and the other along western region of the city known as Shateit River. These two water ways in the south of Shooshtar rejoin again in the Band-e-Qir region to form the great Karoon.
After the Borj Ayar Bridge many waterfalls have been naturally formed extruding the rocks upon the Gerger River. It is said that Valerian the emperor of Rome constructed this bridge. Materials used in the construction are various kinds of stone, and the arch has been designed in an intricate and spectacular form. This dam is approximately 521 m. in length. It has gone under repair during the Qajar period. The same is also reputedly known as the Khaqan Dam.