The
Saka Era was widely used in
Bengal, prior to the arrival of Muslim rule in the region, according to various epigraphical evidence. The
Bikrami calendar was in use by the Bengali people of the region. This calendar was named after king
Vikramaditya with a zero date of 57 BCE. In rural Bengali communities, the Bengali calendar is credited to "Bikromaditto", like many other parts of India and
Nepal. However, unlike these regions where it starts in 57 BCE, the modern Bangladeshi and Bengali calendar starts from 593 CE suggesting that the starting refers the Bengali king
Shashaka's ascent to throne.
Hindu influence Some historians attribute the Bengali calendar to the 7th century Bengali king
Shashanka, whose reign covered the Bengali era of 594 CE. Hindus developed a calendar system in ancient times.
Jyotisha, one of the six ancient
Vedangas, was the Vedic era field of tracking and predicting the movements of astronomical bodies in order to keep time. The ancient Indian culture developed a sophisticated time keeping methodology and calendars for Vedic rituals. The Hindu Vikrami calendar is named after king Vikramaditya and starts in 57 BCE. In rural Bengali communities of India, the Bengali calendar is credited to "Bikromaditto", like many other parts of India and Nepal. However, unlike these regions where it starts in 57 BCE, the Bengali calendar starts from 593 suggesting that the starting reference year was adjusted at some point. Various dynasties whose territories extended into Bengal, prior to the early 13th-century, used the
Vikrami calendar. For example, Buddhist texts and inscriptions created in the
Pala Empire era mention "Vikrama" and the months such as
Ashvin, a system found in Sanskrit texts elsewhere in ancient and medieval Indian subcontinent. Hindu scholars attempted to keep time by observing and calculating the cycles of the Sun (
Surya), Moon, and the planets. These calculations about the Sun appear in various Sanskrit astronomical texts in
Sanskrit, such as the 5th century
Aryabhatiya by
Aryabhata, the 6th century
Romaka by Latadeva and
Panca Siddhantika by Varahamihira, the 7th century
Khandakhadyaka by Brahmagupta and the 8th century
Sisyadhivrddida by Lalla. These texts present Surya and various planets and estimate the characteristics of the respective planetary motion. According to Shamsuzzaman Khan, it could be Nawab
Murshid Quli Khan, a Mughal governor, who first used the tradition of
Punyaho as "a day for ceremonial land tax collection", and used Akbar's fiscal policy to start the Bangla calendar. According to
Amartya Sen, Akbar's official calendar "Tarikh-ilahi" with the zero year of 1556 was a blend of pre-existing Hindu and Islamic calendars. It was not used much in India outside of Akbar's Mughal court, and after his death the calendar he launched was abandoned. However, adds Sen, there are traces of the "Tarikh-ilahi" that survive in the Bengali calendar. The zero year in the Bangladeshi calendar era is 593 CE.
Shamsuzzaman Khan wrote, "that it is called Bangla san or saal, which are Arabic and Parsee words respectively, suggests that it was introduced by a Muslim king or sultan." In the era of the Akbar, the calendar was called as
Tarikh-e-Elahi (). In the "Tarikh-e-Elahi" version of the calendar, each day of the month had a separate name, and the months had different names from what they have now. According to Banglapedia, Akbar's grandson
Shah Jahan reformed the calendar to use a seven-day week that begins on Sunday, and the names of the months were changed at an unknown time to match the month names of the existing
Saka calendar. This calendar is the foundation of the calendar that has been in use by the people of
Bangladesh. ==Calendar structure==