As many as 70 million Hindus and others are expected to converge in this north Indian city for a holy dip in the Ganges over the 42-day long Ardh Kumbh festival commencing January 3.
The festival that comes every six years draws Hindus not only from different parts of India but also from distant countries. It falls mid-way of the 12-yearly Kumbh festival that draws even bigger crowds.
A dip during the period at the holy Sangam, the confluence of Ganga, Yamuna and the mythological Saraswati, is widely believed as a sure way to wash off all sins.
"While people will pour in throughout the festival, there are seven important days that will draw most crowds," fair official Pragyan Ram Misra said.
Besides the opening day, Jan 3 (Paush Purnima), the other auspicious days are Jan 14-15 (Makar Sankranti and the day after), Jan 19 (Mauni Amavasya), Jan 23 (Basant Panchami), Feb 3 (Magh Purnima) and Feb 16 (Maha Shivratri).
According to the official, the opening day is expected to draw about five million people. The largest single gathering would be on the dark night of Jan 19 when authorities expect about 25 million people.
"Making arrangements and ensuring logistics is a gigantic task as the gathering would be by far the largest on the earth," Misra said.
The Shahi Snan, or royal bath, led by thousands of Naga sadhus belonging to 13 prominent Hindu congregations would take place Jan 14, 15, 19 and 23.
These sadhus are known for their unworldly ways and move around without any clothes - throughout their 42-day long stay in camps on the riverbanks and even as they march down in colourful and musical processions for their bath.
Unlike the 12-yearly main Kumbh Mela held in four different places in the country (Allahabad, Haridwar, Ujjain and Nasik), Ardh Kumbh is observed only at Allahabad and Haridwar.
Also at variance from the Kumbh, there is no battle-between-saints-and-demons associated with this fair.
The timing of the festival is governed by the Hindu tradition as well as astronomical configurations.
"Ardh Kumbh commences when Jupiter begins to enter Taurus and the sun as well as moon are in Capricorn. That happens once in six years," said Ram Naresh Tripathi, a renowned Allahabad-based scholar of Sanskrit and Hindu mythology.
"This city of Prayag (old name for Allahabad) has the unique distinction of being right at the centre of the earth, and the sunrays falling directly on the spot during the period generate unique minerals in the water at the holy 'sangam'.
"A dip at the confluence goes a long way in ridding a person of all that is bad," he added.