Buddhism holds a unique place in the history of Indian Buddhism at least for two reasons. First, Bengal was the last stronghold of Indian Buddhism where it survived as a socio-cultural force until the twelfth century AD, despite its disappearance from other parts of the sub-continent. Secondly, it is generally claimed that Bengal was the home of a degenerate form of Buddhism known as Tantric Buddhism. Tantric Buddhism is a later development in Bengal and therefore it remains to be seen what specific factors are responsible for turning the pure form of Buddhism into tantricism and whether the mystic and esoteric practices in the Buddhism of Bangladesh are of distinctively Bengali origin.
It is possible that Buddhism entered Bengal before Asoka's time. After attaining enlightenment, the Buddha is said to have delivered his first sermon at Saranath and then moved to Magadha, Koshala, Vaishali and other places within what was known as Majjhimadesha or Madhyadesha. In the Divyavadana, the eastern boundary of the Majjhimadesha is said to have extended as far as pundravardhana (North Bengal). Furthermore, the Buddha is said to have received considerable support from King Bimbisara of Magadha who not only dedicated Venuvana as a residence for monks, but also remained his close friend and a great patron of his Dhamma throughout his life. Since Bengal was adjacent to Magadha, it is possible that the Buddha had visited parts of Bangladesh as suggested by Hiuen Tsang, who notes that Asoka had erected stupas at various places in Bengal and Orissa to commemorate these visits.
Asoka's Reign and the Post-Maurya Period Epigraphic and other sources reveal that Buddhism had established a powerful footing in Bengal during Asoka's reign. The discovery of a Mauryan inscription in Brahmi characters at mahasthan in the district of bogra bearing the name Pudanagala (Pundranagara) and the recovery of many Mauryan coins and other artifacts dating from the fourth and third centuries BC suggest that the Gangetic delta was under the control of the Mauryan empire.
With the fall of the Mauryan Empire, Buddhism lost its royal patronage.
Buddhism received a further impetus from the Kushanas in the first century AD when Kaniska raised Buddhism to the status of a state religion, erected stupas and chaityas, built monasteries and, like Asoka, sent missions abroad. The discovery of Buddha images, copper and gold coins and inscriptions also clearly throw light on the flourishing condition of Buddhism during the reign of Kaniska.
After Harsavardhana, the Khadga dynasty is said to be the first Buddhist dynasty to rule an independent Bengal between the 7th and 8th centuries AD. The discovery of two copperplates, one at Ashrafpur, 30 miles north-east of dhaka and another at Deulbari, 14 miles south of Comilla, gives us valuable information about this royal dynasty.
Rule of the Pala Dynasty The Pala rule may be regarded as the golden age of Buddhism in Bengal. The Palas were devout Buddhists (Parama-saugata) who were, however, equally sympathetic to other faiths. They invoked the Buddha at the beginning of their official records. Buddhism survived and flourished in Bengal for four centuries under the patronage of the Pala kings, while it was almost wiped out in other parts of India. At the same time, it also became a dominant international force, extending its influence to Tibet in the north and the Malaya peninsula in the south.
Dharmapala is also known to have built a monastery at Somapura, in Rajshahi district. The somapura mahavihara, Naogaon which became a model for many monasteries in South-east Asia, stands as a magnificent testament to the Pala patronage of Buddhism. Dharmapala is also said to have established as many as fifty religious schools designed to teach Buddhist philosophy and to study Prajnaparamita in particular. He was a great patron of the Buddhist writer, Haribhadra, and, during his reign, as in his father's, many distinguished Buddhist teachers, such as Purnavardhana, Prabhakara, Kalyanagupta, Sagaramegha, Bhuddhajñapada, flourished.

Buddhism flourished during the reign of the Chandra dynasty in harikela (eastern and southern parts of Bengal). The discovery of a large Buddha stupa, Salbana Vihara and other inscriptions at the Mainamati hills, four miles to the west of Comilla, still bears testimony to the condition of Buddhism during the Chandra kings.

This mystic form of Buddhism developed in Bengal during the Pala period and its profound impact entirely changed the course and history of Buddhism. This medieval Buddhist movement was founded by the tantric acharyas known as Siddhas who are traditionally believed to be men of psychic and supernatural powers.
The decline of Buddhism, however, did not result in its total disappearance from the land of its birth, and it continued to survive in various forms of popular worship, rites and rituals until its resurgence in modern India. With its rediscovery in its parent country, the traditions of Buddhism were significantly recognized so that the Asokan pillar, the sacred Wheel of Law (Dharmachakra) and the Singhanada sculpture from Saranatha are now a part of Indian national life and heritage. The renewal of Buddhism in India today is attributed to Dr BR Ambedkar, the architect of the Indian Constitution, who led the mass conversion of millions of untouchables or 'Scheduled Castes' to Buddhism in 1956. In Bengal, however, the revival of Buddhism seems to have taken place centuries before Dr BR Ambedkar's introduction of the neo-Buddhist movement in Maharastra and other places. In the districts of chittagong and the chittagong hill tracts, the south-eastern parts of Bangladesh, a Buddhist minority had been practising Theravada long before the Moghuls and the British arrived in Bengal. In course of time, these Buddhists reformed their Sangha and in 1887 founded the Chittagong Buddhist Association, believed to be the first Buddhist society to be formed in the sub-continent.