As described when describing aryanization of bengal, the hindu religion penetrated into bengal in slow steps in the ancient period; and probably not till the gupta phase. This hindu religion was, however, not an adoptation of a foreign Indo-european religion: rather its peculiar Indian, and in particular, Bengali, form is likely to have been born out of a large amount of mixture of the Indian and local religions and beliefs.
Nevertheless, many of the aspects of current Bengali Hindu religious life, as well as the introduction of buddhism and jainism, dates back to the period before the guptas. The vedic religion made their strong entrance into Bengal during and immediately succeeding the gupta period. The Pala and Candra period saw wide tolerance for religion, and was the golden age of Buddhism in Bengal. This was followed by the period of Sena rule which saw the real establishment of pauranic hinduism here. At the end of this ancient period, Islam had barely started growing roots in Bengal.
Up to history of ancient Bengal