Arg Alishah or Arg of Tabriz, it’s a southest wall of citadel which backs to ilkhanid dynasty (14 century).
Some stories said it was a mosque here and in Qajar dynasty it has used as prison.
still it is a huge structure and visitors can visit it during the day.
The most important point for the building was that its vaulted ayvan was larger than the famous historic vault of Chosroes/Kisra or the Taq Kisra at Ctesiphon/Mada'in.
this monument was registered as National Monuments of Iran in 1933.
Definitely it has worth to visit.