Bab al-Hadid (or the Iron Gate) was originally planned during the reign of al-Zahir Ghazi and built by his son Muhammad as Bab al-Qanat (the Aqueduct Gate). It was rebuilt by the final Mamluk sultan Qansuh al-Guri in 1509. It holds an unknown shrine within its walls.
Tabbaa, Yasser. Constructions of Power and Piety in Medieval Aleppo, 20-21. University Park, PA: The Pennsylvania State University Press, 1997.