The Bengali calendar was originally known as Tarikh-e-Elahi. It was introduced on the 10th or the 11th March in the 29th year of Akbar's reign (1585 A.D.). It, however, dates from the day of Akbar's ascension to the throne of Delhi and commemorates his coronation as the Emperor of India in 1556. The Second Battle of Panipath and the Coronation of Akbar as the Emperor of India were important events in Mogul history. The Moguls had nearly lost the throne of Delhi for good. Akbar was not even an adult when the life of Humayun was suddenly cut short on the stairs of his own library. It was to glorify and immortalize these historic events, and also to facilitate the collection of revenue during harvest in a more systematic way, that Akbar the Great introduced the Tarikh-e-Elahi calendar the 10th of Rabiul Awal in 963 A.H.
Akbar saw the need of introducing a uniform scientific, workable and acceptable system of calculating days and months through a reformed calendar. With this end in view, he commissioned Amir Fathullah Shirazi, a distinguished scientist and the most famous astronomer of the day, to make a recommendation for the reformed calendar. Abul Fazal, the renowned scholar and a minister of Akbar the Great, in his scholarly work Akbar Namah, gives details of the events leading to the new era under the Royal Forman of Akbar. Abul Fazal explains that the use of the Hijrah (Hegira) Era was unfair to the peasantry, because 31 lunar years were equal to 30 solar years and the revenue was collected on the basis of lunar years whereas the harvest depended on the solar ones. Abul Fazal was right because the lunar year consists of 354 days and the solar years has 365 or 366 days. Thus there is difference of 11 or 12 days between the lunar and the solar years.
The Forman (Royal Proclamation) ran as follows: "In this dominion adorning time and auspicious epoch, when a Qarn (cycle) of the victorious session on throne of sovereignty has elapsed, and good day of fortune has begun to smile, a world obeyed". Forman was issued to the effect that the governors of the Imperial dominions, and the other offices of state and finance, who in accordance with their degrees and positions, are recipients of the royal favours, should know as follows:
Suppose, for example, someone makes a contract, or takes a favour or a loan, and the period of execution be 4 years, 4 months: unless the exact date of the beginning be known, it will be difficult, or rather impossible, to determine the date of completion. It is event too that whenever an era has prevailed for a long time, the establishment of a new one opens the gates of ease and prosperity for all mankind.
The repeated representation of this body of men, and regard for their positions, prevailed and were accepted, and an order was issued that the new year, which followed close on the year of ascension, should be made the foundation of the Divine Era, and that the gates of joy and comfort should be opened.
Also that in the almanacs of India they (the almanac writers) should enter this new era instead of their discordant eras ... and that they do away with their various eras. And whereas in the almanacs current in India the years were solar, and the months lunar, we ordered that the months of the new era should be solar.'
Abul Fazal eulogises the Forman of 992 A.H. (1584 A.D.) in the following way: The pillar of the founders of the Sacred Era was the learned of the age, the Plato of cycles (Alwani) Amir Fathullah Shirazi whose title was Azad-ud-Daula. It was he who in a happy hour laid the foundation of this heavenward soaring edifice. Although the foundation (i.e. the Forman) took place in 992 A.H. yet the position of events dates from the beginning of the sacred accession of Akbar.
He further adds: The Forman ordered that the new year which followed close on the year of accession should be made the foundation of the Divine Era and accordingly the first of Muharram (the first month of the Hegira calendar) of 963 A.H. being close to the historic occasion was also made the starting point of the Tarikh-e-Elahi." Since the month of Muharram coincided with the Bengali month of Baishakh in 963 A.H., the month of Baishakh in Bengal was made the first month of the Bengali Era instead of the month of Chaitra which was the first month of the Shaka Era being practised in the then Bengal.
The months of the new Bengali Era (or Tarikh-e-Elahi) were initially known as Karwadin, Ardi, 'Vihisu, Khordad, Teer, Amardad, Shahriar, Aban, Azur, Dai, Baham and Iskander Miz. Nobody knows for sure how and when we started naming the months as Baishakh, Jaishtha, etc. It is presumed that these months, based on the names of the stars, were derived from the Shakabda which was introduced in 78 A.D. to commemorate the reign of the Shaka dynasty in this subcontinent.
The star-based names of the months were derived as follows:
Some claim inadvertently that the Bangla calendar was introduced by Shashanka, king of Bengal, to commemorate his conquest of Assam. But records testify to the fact the Shashanka, son of Maha Sengupta, conquered Benaras and moved towards Chilka lake and never towards Assam.
The system of celebrating Nababarsha or Pawhela Baishakh (1st of Baishak) was also introduced by Akbar the Great. After introducing Tarikh-e-Elahi, he abolished the hitherto practised Muslim festivals and replaced them by 14 new festivals, one of which was Nawroze or the celebration of the New Year's Day. It was the celebration of Nawroze which enabled Prince Selim (later emperor Jehangir) to meet and fall in love with Meherunnisa (known as Nurjahan in history). It was again in one such Nawroze festival that the Prince Khurram (known as the Emperor Shahjahan in history) first came across Mumtaz Mahal, whom he immortalised through the great "poetry in marble" known the world over as Taj Mahal. Had there been no Nababarsha (or Nawroze) festival, there perhaps would be no Nurjahan, and no Taj Mahal.