The character of Bengal is largely determined by the Ganges and Bramaputra rivers which divide into innumerable branches before entering the sea. Although the area is currently divided between the two modern states of India and Bangladesh it retains a certain homogeneity based on its language (Bangli) and culture.
In the thirteenth century the region was conquered by Muslim Turks who occupied the city of Gaur (Lakhnaw) in north-west Bengal. From this base the areas of Satgaon (south-west Bengal) and Sonargaon (east Bengal) were conquered and incorporated into an independent sultanate in 1352 CE by lliyas Shah. Despite dynastic changes the area remained independent until the sixteenth century when it was incorporated into the Mughal sultanate, and even then it still retained its identity as a separate province.
Lack of suitable building stone in the area meant that the predominant materials of construction were red clay bricks from the alluvial silts and bamboo and thatch. The majority of buildings were made of bamboo and thatch and consist of a rectangular area which is roofed by a curved thatch roof ('charchala' and 'do-chala'). Most of the more important buildings, however, were made out of brick. In the pre-Mughal period such buildings were faced either with red terracotta plaques or less frequently in stone. From the sixteenth century onwards brick buildings were coated in white plaster.
One of the achievements of Bengali building was its translation of traditional bamboo and thatch architecture into more permanent stone and brick forms. One of the best examples of this is the use of curved roofs from the sixteenth century onwards. There are two main forms of this roof - do-chala and char-chala. A do-chala roof consists of a central curved ridge rising in the middle with curved side eaves and gabled ends. A char-chala roof is made of crossed curved ridges with curved eaves. The earliest surving example of this roof type in a brick building is the tomb of Fath Khan at Gaur dated to the seventeenth century. This form was so successful that it was used elsewhere in the Mughal Empire, at Agra, Fatehpur Sikri, Delhi and Lahore. In addition to its aesthetic appeal curved roofs also have a practical purpose in an area of high rainfall.
Other characteristic features of Bengali architecture adopted by the Mughals and used elsewhere are the two-centre pointed arch and the use of cusped arches for openings.
The predominant form of Islamic architecture in Bengal is the mosque. In pre-Mughal Bengal the mosque was virtually the only form of Islamic building, although after the sixteenth century a wide variety of Islamic building types such as the caravanserai and madrassa were introduced. Characteristic features of Bengali mosques of all periods are multiple mihrabs, engaged corner towers and curved cornices. Although multiple mihrabs sometimes occur in North India, Bengal is the only place where they are a constant feature in mosques. The number of mihrabs is determined by the number of entrances in the east wall. Engaged corner towers are a constant feature of Bengali architecture and may derive from pre-Islamic temples. Curved cornices are probably derived from the curved roofs of bamboo huts; it is possible that they may have a practical function for draining water away from the base of the domes.
During the pre-Mughal sultanate three types of mosque were built, rectangular, square nine-domed and square single-domed.
Mosques built on a rectangular plan are divided into aisles and bays according to the number of domes on the roof. At the east end of each aisle is a doorway and at the west end a mihrab. There are also openings on the south and north sides of the mosque corresponding to the number of bays. The nine-domed mosques are similar to those found elsewhere in the Islamic world, but they differ in having three mihrabs at the west end. The most popular form of mosque in pre-Mughal Bengal was the single-domed chamber. It is likely that this design is developed from the pre-Islamic temple of Bengal.
None of these early mosques was equipped with minarets and sahns as was common in the Middle East but these features were introduced with the Mughal conquest in the sixteenth century. However, the Mughals were also influenced by the local architecture of Bengal and it is from this period that we have the first example of a do-chala roof translated into brick (the Fath Khan Tomb at Gaur, dated to the seventeenth century).
Muslim buildings can be found all over the region of Bengal, although the largest concentrations can be found at Dhaka and Gaur (Lucknow). Calcutta, the capital of Indian Bengal, was founded during the period of British rule in the nineteenth century. As might be expected the early mosques of the city show strong British influence. The descendants of Tipu Sultan built three mosques in the city all with the same double-aisled, multi-domed rectangular plan. The most famous of these buildings, the Tipu Sultan Mosque built by his son Muhammad, is built in the style of a European building with Tuscan colonettes and Ionic columns used for the windows and central piers.