The Tughlaq tombs of Delhi - simlicity in style, but functional

During the early Muslim rule in India, much attention was not paid to the look of various structures like tombs mausoleums, etc built by them. They were content with minimum decorations in the buildings which were more functional in nature than  mere show pieces of splendid architecture. In this respect, the tombs built by the rulers of the Tughlaq dynasty (1320–1413) in India  are  known for their simplicity and not grand in style.  Their monotonous and heavy structures  are a blend of Hindu and Islamic style. They  were not great builders with an eye on the grandeur and beauty of the structures. Their buildings look  big forts and and massive; no attention was paid to interior or exterior decorations, thus their tombs differ from those built by other Muslim  rulers.  Though there are Hindu elements in their buildings, they lack the influence of  Hindu temple architecture and craftsmanship. In the later period Lodi and Mogul rulers liberally mixed the Hindu design. In the case of Tughlaq buildings. the Hindu influences were limited to  the flat lintel instead of pointed arch, pillars, windows with balconies and eaves and railings.
Ghiyath al-Din Tughlaq's Tomb In Delhi 
The Tughlaq rulers  focused on three types only when building tombs.They are:  square, octagonal and pavilion. The last one being simple includes  a pavilion or a chhatri. Chhatri design is a common architectural feature in Rajasthan, patronized by the Rajput rulers and nobles. In the case of Tughlaqs, they built simple tombs for the  nobles and family members of the sultans. 

The Founder of Tughluq dynasty of the Delhi Sultanate, Ghiyas ud-Din Tughluq,  in a short period of his reign,  was keen to have a new fortified capital  city called Tughluqabad built close to Delhi. Three years later, back in Delhi, being a Sultan now,  he wanted to build a tomb for himself in the new capital (ignoring the one he built  in Multan when he was the governor there). After his  unexpected death, his successor Muhammad bin Tughlaq,  for administrative reasons and better  amenities, shifted the capital back to Delhi leaving the newly built Tughluqabad to rot  and  crumble.  Ghiyas' tomb is  still there and is  in good condition. The later rulers never shifted the tomb of Ghiyas to Delhi. 

Built in 1325 using  red sandstone and white marble, the structure has a marble dome, believed to be one of the earliest masterpieces  made of a fine combination of red sandstone and white marble. The square tomb in the center of a pentagonal enclosure with high walls can be accessed through entrances on the north, east and south sides.  The unique feature is this building does not have minarets, commonly found in many Islamic-styled edifices.  There are no Minarets surrounding the tomb. The builder got the inspiration from  the Khalji portal- Alai Darwaza- in the Qutb Minar complex.  Ghiyas was originally a Khalji slave who later became one of the governors.
The sloping walls, at a 75 degree angle with the ground instead of vertical walls is new architectural style ever tried before  and is quite  similar to the sloping walls of the Hindola Mahal (Swing palace) in Mandu, Madhya Pradesh.  The distinctive sloping walls  give an impression that the palace is swaying from side to side.  The idea behind the sloping wall is to give extra strength to the building and to buttress the heavy stoned arches that support the ceiling. The inner  walls are vertical and plain.

The presence of a kalassa (pinnacle) atop the white marble dome and a redundant stone lintel installed just below the arch shows the influence of Hindu design. Atop all Hindu Temples - both ancient and modern - on the Vimana you can see the Kalasa (the numbers vary). They come alive during consecration ceremony (Kumabhisekam).
graves inside. Ghiyath al-Din Tughlaq's Tomb In Delhi 

The pinnacle was planted at the apex of the Tughluq dome. The  purpose of  stone 
lintel is  to ensure stability, to fit a rectangular timber door in the arched opening. It could be for decoration or aesthetic purposes.  Regardless of its utility, this elegant feature appears to be an  effective device in the building style of the Tughluqs as well as their successors. 
There are three graves in the Ghiyas tomb  The central grave is that of  
Ghiyath al-Din Tughluq, other two belong to his son, Muhammad bin Tughluq and 
his wife, Makhdum-i-Jahan. The grave of Makhdum-i-Jahan  was a later addition.