The once-12-years in Maha Kumbh Mela that began in Allahabad, Uttar Pradesh, Monday, is expecting a massive gathering of more than 100 million devotees, god-men and tourists duirng the 55-day mega festival.

The mega festival, where devotees from across the world gather to take a holy dip to attain salvation at the confluence of Ganga, Yamuna and mystical Saraswati rivers, is billed as the biggest human gathering in the world.

The first written evidence of the Kumbha Mela can be found in the accounts of Chinese traveler, Huan Tsang who visited India in 629 -645 CE, during the reign of King Harshavardhana.

However, similar observances date back many centuries, where the river festivals first started getting organised. According to Hindu theology, its origin is found in one of the most popular medieval puranas, the Bhagavata Purana.

Rediff.com takes a look at some stunning pictures of the previous Kumbh Mela festivities.

In this photograph, Naga Sadhus run in to the Ganga to get a holy dip during the 2001 Maha Kumbh Mela in Allahabad.

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A Hindu devotee prays in the Ganga, after taking a holy dip during the 2001 Maha Kumbh Mela in Allahabad.

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Thousands of devotees wait for their turn to bathe in the holy waters of Ganga during the 2001 Maha Kumbh Mela in Allahabad.

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Thousands walk across pontoon bridges over the holy Ganga in Allahabad during the 2001 Maha Kumbh Mela.

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Devotees bathe in the holy Ganga during the 2001 Maha Kumbh Mela in Allahabad.

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A sadhu blows his conch shell as the 2003 Kumbh Mela is declared open on the banks of the Godavari river in Nasik.

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A Naga Sadhu reacts to the camera after taking a dip in the Sangam, the confluence of three rivers, Ganges, Yamuna and Saraswati, during te 2007 Ardh Kumbh Mela in Allahabad.

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Naga Sadhus wait on the banks of Ganga during the 2007 Ardh Kumbh Mela in Allahabad.

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A Sadhu, whose followers say he has not moved his arm and cut his fingernails for 32 years, sits in a camp near the banks of Ganga, during the 2010 Kumbh Mela in Haridwar.

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A Hindu devotee ties his turban after taking a holy bath during the 2007 Ardh Kumbh Mela in Allahabad.

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A Sadhu takes pictures at the 2007 Ardh Kumbh Mela in Allahabad.

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A Hindu devotee offers prayers at the start of 2007 Ardh Kumbh Mela at Sangam in Allahabad.

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A Naga Sadhu prays while taking a holy dip in the waters of Shipra river during the 2004 Simhasta Kumbh Mela in Ujjain.

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Hindu holymen await an auspicious moment before bathing at 2003 Kumbh Mela at Trimbakeshwar in Nasik district of Maharashtra.

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A Sadhu holds a mirror with a picture of a Bollywood actress during 2007 Ardh Kumbh Mela in Allahabad.

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A boy watches the first 'Shahi Snan' (grand bath) at a sacred pond at the 2003 Kumbh Mela in Trimbakeshwar, near Nasik.

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Naga Sanyasis take a dip during the first 'Snahi Snan' at a sacred pond during the 2003 Kumbh Mela in Trimbakeshwar, near Nasik.

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A Hindu holyman dries his robe after taking a dip in the river Godavari at the 2003 Kumbh Mela in Nasik.

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A Hindu devotee holds his son while taking a holy dip in the Ganga during the 2001 Maha Kumbh Mela in Allahabad.

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A Naga Sadhu rides on a horse as he marches for a royal bath during the 2001 Maha Kumbh Mela in Allahabad.

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Pilgrims on the banks of Ganga take a dip during the 2001 Maha Kumbh Mela in Allahabad.