The vast 4000 acre stretch around the holiest of holy Hindu spots -- Sangam  in Allahabad -- looks like a mammoth tent township, ready to host the 42 day-long Ardh Kumbh Mela, which draws crores of devout Hindus not only from across the length and breadth of the country buat also from across the globe.

Lakhs of Hindus have started pouring in to take a dip at the Sangam on Wednesday, the first day of the most popular fair.

What draws them to Allahabad is their unquestioned and absolute belief that a dip at the Sangam - regarded as the holiest confluence of three rivers Ganga, Yamuna and the mythological Saraswati - will wash off all their sins.

The most auspicious time to do this - the Ardh Kumbh Mela held every six years - commences in the early hours of Wednesday and continue over the next 42 days.

A total of about seven crore Hindus are expected to converge in Allahabad.

As many as about two lakh persons were stated to have already arrived in the camps along the river banks, while several hundred thousands more were expected to arrive by Wednesday morning.

"The bathing will begin from 4.30 am and continue through the day," distrct magistrate and head of the Ardh Kumbh Mela operations P R Misra told a news conference on Tuesday evening.

"According to our estimates, about 25 lakh people will participate in the first holy dip of the festival on Wednesday," he said. "But that is the smallest number as compared to the estimates for any of the other six most auspicious days during the festival."

Misra claimed, "Of the total of seven crore persons estimated to participate in the entire festival that draws the single largest human gathering on earth, about 2- 2.5 crores are expected on just one day - January 19  (Mauni Amavasya) - while half 50 lakhs to a crore are expected on the other important days - January 14 ,15, 19, 23 , February 3 and 16."

Unlike the main Kumbh, which is celebrated in four different destinations across the country � Allahabad, Haridwar, Ujjain and Nasik every 12 years, Ardh Kumbh is observed only at Prayag and Haridwar.

Also at variance from the Kumbh, there is no mythological legend -- like the battle between the saints and demons -- associated with this fair. 

The timing of the festival is governed not merely by Hindu mythology, but is also guided  by astronomical configurations.

"Ardh-Kumbh commences when Jupiter begins to come into Taurus and the sun as well as moon are in Capricorn -- and that happens only once in six years," pointed out Prof Ram Naresh Tripathi, a well-known Allahabad-based scholar of Sanskrit and Hindu mythology.

"This city of Prayag (the ancient name of Allahabad) has the unique distinction of being right at the center of the earth; and sunrays falling directly on this spot during the period generate unique minerals in the water at the holy sangam to rid people of not just sins but also disease," he said.

A vast area of about 4000 acres stretching about 8 kilometres along the Ganga and Yamuna river banks stands virtually converted into a giant tent township.

"We have created a huge infrastructure, which includes laying of about 76 km of thick steel chequered plates to serve as convenient walking paths on the river banks for the pedestrian traffic that will be seen from Wedmesday," said Misra.

"Movement of all types of vehicles will remain restricted in the entire Mela area on the key bathing dates and even pedestrian traffic will be highly regulated to avoid a stampede, which could be disastrous," he said.

As many as 38 new tubewells have been installed to maintain water supply in the entire Kumbh township, where some 456 km of drinking water pipelines have been laid.

Besides a  'fully-equipped' makeshift 100- bed hospital, 14 primary health centres have been created to cater to minor health needs of  visitors.