The Kalan Mosque ("large mosque") in Nizamuddin is one of the mosques built in Delhi by Khan-i Jahan Junan Shah, vizier to the Tughluq Sultan Firoz Shah (r. 1351-1388/751-789 AH). Scholars attribute between two and seven mosques to the patronage of the vizier; three are generally considered to be his commissions, the Khirki Masjid in Tughluqabad and the Kali or Kalan Mosques of Firuzabad (Shahjahanabad) and Nizamuddin, both contained within modern-day Delhi.
The Nizamuddin Kalan Mosque, popularly called the Kali Mosque, is located at the eastern periphery of Nizamuddin and is completely surrounded by dense urban fabric. It can be dated to 1370-1371/771 AH and attributed to Khan-i Jahan Junan Shah by an inscription on the mosque's east gate. Of its three entrances, the main gate resembles those of the Khirki Mosque and the Kalan Mosque in Shahjahanabad.
The mosque has a square plan measuring approximately 27 meters per side. Described by Nath as having a caturangana, or four-quartered typology, it is organized around four rectangular internal courtyards in each quarter of the plan. Although the dominant typology for congregational mosques of the period was that of a large central courtyard surrounded by covered arcades on three sides and the larger prayer hall along the west (qibla), the Kalan Mosque represents a variation whereby most of the mosque is roofed and four smaller courtyards allow for light and ventilation. The Khirki Mosque, built a few years later, is a more refined variation of this four-courtyard type. Notably, these two mosques are the only covered mosques found in northern India.
The mosque is entered from three projecting domed gateways centered in its eastern, southern and northern sides. Square in plan, the gates are further defined by tapering bastions (minars) at the corners that rise 1-2 meters above the level of the merlons decorating the top of the wall. The mosque walls are battered on the exterior and vertical on their courtyard elevations; some of the exterior walls are maintained plastered and painted white.
The roofed portion of the mosque is divided into square bays of equal size, each topped by a small dome. From within, the domes appear hemispherical, and their external appearance is conical. Continuous arcades, one bay deep and eleven bays per side, run along the eastern, southern and northern walls. An interior arcade, also one bay wide, runs east-west and north-south, dividing the building into four quadrants. Both the outer and the inner arcades are composed of pointed arches springing from double stone pillars. The lack of a central dome in the mosque plan creates a nonhierarchical space, based on the repetition of columns, arches, and small domes. The prayer hall, which is three bays deep, runs along the western side.
Much of the exterior and most of the interior surfaces have been plastered and painted; where the exterior walls have been left exposed, the underlying rubble masonry is visible. During renovation work carried out at the beginning of the twentieth century and subsequent maintenance, new concrete columns were added to the structure. Over time, many of the original Tughluq elements of the building have been lost.
The Kalan Masjid is still used as a congregational mosque, particularly by the residents of the Nizamuddin neighborhood.