Lat Ki Masjid is the main mosque of the palace complex and is located to the east of the South Court opposite the Talaki Gate. It is one of the most embellished of mosques built by Firoz Shah. It is distinguished with its lithic pillar and square chamber. Unlike usual mosques, it is ‘L’ shaped in plan and its larger side runs north-south. The mosque is called after the lat, an ancient column re-erected in the north-east of its courtyard. The mosque is one of the better known monuments of the Hisar. The column is in the form of a tapering cylinder in four registers, with a finial and an iron rod set in the top, making it about 13.75 m. high altogether. The lower register is reused ancient shaft in a single piece of yellow stone, about 3.30 m. high.
In the Lat Ki Masjid column, above the ancient shaft are drums of red sandstone in three registers, with contrasting bands of red and white stone. The building as it stands today has a prayer hall on the western side of a courtyard, and the remains of a northern wing. There is a square domed chamber on the eastern side of the courtyard. The walls of the mosque are of blocks of sandstone up to the level of the springing of the vaults, but the upper pats of the walls, as well as the vaults and the roof are of baked red brick covered with plaster. This is one of the rare examples of a Firoz Shahi building in which brick is used. The monolithic pink sandstone columns supporting the arches in prayer hall may be reused material from ancient Indian temples.