The Kalan Mosque was built between 1368 and 1387 by Khan-i Jahan Junan Shah, who was a vizier in the court of the last Tughluq sultan Firoz Shah Tughluq. Firoz Shah was a very creative builder which is evident in his display of public buildings, palaces and other pleasure retreats. His works also include the first canal built in the northern part of India, the foundation stone of Firozabad city that was laid in the year 1354. The remains of the ancient city walls remain even today.Kalan Mosque is also sometimes referred to as the Kali Masjid because of its dark appearance.The Mosque was built with a design similar to a citadel, which was built in order to protect the worshippers from external attacks.Two tall towers are present in the mosque near the entrance and the 66 ft mosque is accessed by a flight of 32 steps. The walls of the mosque are very thick and there are around 30 domed bays that form a cloiser. Near the mosque is the Firozabad Railway Station. The prayer hall in the mosque consists of around 15 domed bays organised in the form of five rows and three aisles. The dome, which is shallow and pointed, rests completely on the pointed broad arches with small vaults in the transition zone. The broad arches rest on the square shaped stone piers, are white in colour with the inner surface of the dome being bright green in colour, and plastered. The ancient decoration of the mosque is now hidden under the plastered bands and panels that have now been painted to showcase the individual elements of the building. The predominant colours that have been used in the mosque are green, white and aquamarine blue while the outer walls are the only portion of the building that is still exposed.