Ghiyath al Din Tughluq Shah I (r. 1320-1325) was the first Tughluq ruler who, upon succeeding the Khaljis, established the Tughluqabad Fort on the southeastern side of the Qutb complex in old Delhi. Built during his lifetime, his tomb is a fortress-like complex, constructed on an (now-dry) artificial lake, which separates the tomb from the Tughluqabad Fort. A 229-meter-long causeway, supported by 26 arched piers, crosses the lake to connect the tomb to the fort. Water also added a dimension to the paradise imagery in tomb architecture, a theme that would be carried on from the Tughluq tombs to reach its height with Mughal architecture.

The tomb complex has an oblique pentagonal plan with a battlement perimeter wall supporting conical bastions at each angle. Measuring 11.75 meters in height, the perimeter wall inclines inwards and has a continuous crenellated parapet. One enters the court through a strategically staggered, decorated entrance gate. Arched corridors and vaulted chambers run along the interior side of the court perimeter wall.

Placed diagonally within the court, the tomb itself is constructed of rubble masonry, unadorned on its exterior and faced with red sandstone and a white marble decorative course on the interior. Square in plan, its battered walls are massive: the interior tomb walls measure 11.74 meters in length (18.74 meters on the exterior), with an overall height of 24.4 meters and a 75 degree slope.
Its pointed dome, which rests on a transition of corner squinches, has an an interior diameter of 10.41 meters and an exterior diameter of 13.41 meters. Crowned with a vase and melon (kalash and amala) finial, the dome follows the typology of Hindu temples in the Delhi region. Three sides (north, south, and east) of the tomb have horseshoe-arched doorway openings with spearhead extrusions in their intrados and are flanked by a niche on either side. A marble band begins at the base of these horseshoe arches, running across the architrave. The western wall of the tomb accommodates the mihrab.

The interior of the tomb is faced in red sandstone up to the base of the dome, above which it is clad in white marble. Three tombstones are housed within the tomb structure itself. With the exception of the marble-clad mihrab, the interiors are unplastered and undecorated. In addition to the grave of Ghiyath al-Din, the tomb also contains the graves of his wife Makhdima-Jehan, and his son Sultan Muhammad Adil Tughlaq Shah (d. 1351).

Sources:

Alfieri, Bianca Maria. Islamic Architecture of the Indian Subcontinent. London: Laurence King Publishing, 2000. 37-39.

Asher, Catherine B. Architecture of Mughal India. Cambridge and New York: Cambridge University Press, 1992. 8.

Nabi Khan, Ahmad. Islamic Architecture in South Asia: Pakistan - India - Bangladesh. Oxford, New York: Oxford University Press, 2003. 78-80.

Nath, R. History of Sultanate Architecture. New Delhi: Abhinav Publications, India, 1978. 52-55.

Sahai, Surendra. Indian Architecture: Islamic Period, 1192 - 1857. New Delhi: Prakash Books India, 2004. 26-27.

Welch, Anthony and Howard Crane. "The Tughluqs: Master Builders of the Delhi Sultanate," MuqarnasI (1983): 129, 142-143.