It was around 610 AD that the prophet Muhammad (c. 570 -632) heard God's message for the first time in Arabia, in the city of Makka. His teachings disseminated rapidly as Islam grew into a world religion ruling from Spain to the Central Asia by the 8th century. Its essence is the ideal that God is one and every person is equal before God.
As Muslims worshipped with prostrations before God five times a day obligatorily, the Islamic Empire needed mosques for the congregational worshipping at each area they subjugated. The first mosque was the Muhammad's house in Madina, to which he moved from Makka in Arabia. However, since the earliest monumental buildings were built in Damascus, Syria and Jerusalem, they were much influenced by Byzantine architecture that had been flourishing there. When they got to Persia (now Iran), Egypt, and Spain, they developed architecture suitable for each region under the influence of each tradition.

Although Islamic invasions to India had occurred intermittently since early times, they had been temporary occurrences. It was in 1206 that Islamic political power was established in India for the first time, by Kutb al-Din Aibak.
After that, five dynasties appeared in succession in Delhi and the kings named themselves Sultans of Delhi, so those dynasties are called 'Delhi Sultanate' as a whole. Their governing people were Turkish or Afghan nations, but culturally Persia had been ruling Central Asia from Iran, Islamic architecture brought to India was Persian Islamic architecture too.

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A muslim worshipping in a mosque

At the end of the 12th century when the first Indian mosque was to be constructed in Delhi, India had been developing stone construction for thousands of years and its technology and aesthetics had almost reached the stage of perfection.
Their religious backgrounds were Buddhism in ancient times, Hinduism and Jainism in the medieval period. As they were born in the same region and grew under the same climate, they did not have architectural differences basically.
However, Islamic architecture had grown under a completely different civilization and was alien architecture to India, having principles and sense of beauty totally different from Indian traditional architecture.

The Sultans and ministers were well-grounded in their own architecture and wanted to build mosques and palaces same as in their home countries. Since craftsmen who constructed those buildings actually were conquered Indians, it was to cause strong entanglements between traditional and foreign architecture.
Then, what was the difference between Indian traditional architecture and Islamic architecture coming from the outside? Before seeing that, I will expound three categories of world architecture.

The first category is the 'Sculptural architecture' that treats buildings as massive objects and elaborates their sculptural effect as architectural expression. It is represented by the Indian traditional architecture. As typically seen in temples in Khajuraho, not only are their walls completely covered with statues of Gods and other sculptures but also the building itself is regarded as an enormous sculpture as a whole. On the other hand, their interior spaces are quite narrow and inferior as compared with its majestic exterior.

 
Left : Vishvanatha Temple in Khajuraho, India
Right : Umayyad Mosque in Damascus, Syria

The second is the 'Membranous architecture' or 'Enclosing architecture' that to the contrary emphasizes their interior spaces or courtyards above all and relegates their exterior forms to second place. It is represented by Islamic architecture. The Great Mosque in Damascus and the Friday Mosque in Isfahan are buried in the fabric of town houses and stores, and we therefore cannot see their external forms at all. However, once inside the mosques, we shall find well-regulated composition and ornament in geometric order and worship halls as magnificent interior spaces.

The third is the 'Framework architecture' or 'Trabeated architecture' that consists of a post-and-beam frame and its upper roof, not necessarily requiring demarcation of space with walls. Japanese wooden architecture is typical. Inside and outside spaces become continuous as a result of the lack of walls, and its sculptural effect of an exterior form is not so strong.

As the political power of Islam in India gradually expanded its dominions from Delhi and constructed mosques in each region, sculptural architecture as the first category and membranous architecture as the second category conflicted with and influenced each other through trial and error. Here Islamic architecture brought from Persia would transfigure with Indianization. We will now glance at the difference between their masonry systems supporting its architecture.

Before the development of 'Sculptural architecture' by the use of stone in the Middle Ages, wooden architecture was the mainstream for the ancient India. As wood decreased afterward due to the aridification of the Indian subcontinent, monumental edifices came to be constructed of stone. However, in spite of using stone, Indians who had been totally involved in the trabeated structure and the aesthetics of wood would continue to persist in trabeation, that is to compose buildings with the post and beam method, treating stone as if it were wood.
Since stone is strong against a compressive force but weak against a tensile force, it is not suitable to be used as a horizontal structural member (beam and lintel). Nevertheless Indians persisted in the trabeated structure, with the development of which they eventually achieved even the realization of enormous temples. However they could not build a large span of interior space with that techniques, having to stand many columns like a grove in large halls.

On the other hand, since there was little wood in the Middle East from its inception, they erected buildings of brick or stone, inventing the masonry structure of arch and dome since early in the ancient age. The arch is a device to stride a large span by stacking stone pieces (voussoir) radially along a circular arc, with which one can cover a large hall of dozens of meters in diameter without columns. Islamic architecture born in the Middle East made possible the erection of all kind of buildings in the membranous way freely using that principle of arch and dome.

 
Jain Temple at Kumbharia, Quwwat al-Islam Mosque in Delhi

The first mosque in India, Quwwat al-Islam Mosque in Delhi, was also built as a series of arches and domes. But Indian craftsmen who did not know the principles of true arch and true dome and how to construct them used another method of corbelling, which is to pile up ashlars horizontally, making progressively higher protruding layers. Consequently, most of those unstable corbelled arches and domes have collapsed, leaving a few arches and cloisters constructed in a traditional Indian manner intact up to the preset.

Indian architects and craftsmen though gradually became versed in the techniques of true arch and dome, and consequently built mosques, madrasas (schools), palaces, and caravanserais, using them freely. At long last they were able to realize an outstanding piece of 'membranous architecture' as a dome structure in diameter of as large as 38m without even one column.

Cross section of Gol Gumbaz in Bijapur, India, 1659
(From "Bijapur and its Architectural Remains" A.S.I. Report, Imperial Series vol. 37�j

During the ages of Delhi Sultanate, enough of the construction techniques of Islamic architecture were transplanted to India even though some of the roughness remained. Indian Islamic architecture would reach the summit in the era of the Mughal dynasty from the 16th to 17th centuries.
Its first realization was the Mausoleum of Humayun, the second emperor, which became the prototype of tomb architecture for subsequent Mughals. Its formation is such that in the center of a huge 'Charbagh' (four quartered garden) a large square platform is built, on which a mausoleum with identical facades for its four sides stands symbolically and is capped with a large dome of white marble. It was in India among the vast Islamic areas that this form of tomb architecture was especially loved and made great developments, there is a reason for that;

Generally Islamic architecture is represented by mosques in every region. Persian architecture inherited 'Iwan' from ancient palace architecture as a square shape framing a large arch opening, inside of which is vaulted half-exterior space, and Persian mosques have four iwans facing each other around a courtyard, that is the form of 'Four Iwans.'

Plan of a "Four-iwans-type" Mosque
(Ffrom "Islamic Sacred Architecture" by Jose Pereira, 1994�j

However, as for Indians who loved 'Sculptural architecture,' such introverted buildings with obscure exterior view was not a satisfying form. Then they developed extroverted building in order to enlarge sculptural effects, settling those four iwans facing in opposite directions, back to back, and covering the central space with a symbolic dome. This form is more suitable for mausoleums than mosques and it reached the peak at the magnificent Taj Mahal in Agra.
This was also applied to mosque architecture, projecting the prayer hall among the four sides of courtyard as if it were an independent sculptural building.

Jami Masjid (Friday Mosque) in Delhi

There was an emperor among the Great Mughals who intended more positively to merge Indian tradition with Islamic architecture. He was the third emperor, Akbar (1542-1605). He vastly extended his territory to fit the name 'Empire' and practiced a policy of concord among many Indian religions to make the Empire stable.
As a reflection of this, for buildings in Fatehpur Sikri that he constructed as a new capital and his own mausoleum at Sikandra he seldom used arches and domes and deliberately used traditional posts and beams in spite of being Islamic architecture. A pavilion in Fatehpur Sikri protruding even stone slab eaves protecting against the rainy season looks as it were wooden structure.

 
Akbar's Tomb at Sikandra and a Chatri in the Taj Mahal precinct