(A Sadhu or a Hindu holy man applies ashes on his body after taking a dip during the first ‘Shahi Snan’ (grand bath) at the ongoing “Kumbh Mela”, or Pitcher Festival, in the northern Indian city of Allahabad January 14, 2013. REUTERS/Jitendra Prakash)

Upwards of a million elated Hindu holy men and pilgrims took a bracing plunge in India’s sacred Ganges river to wash away lifetimes of sins on Monday, in a raucous start to an ever-growing religious gathering that is already the world’s largest.

Once every 12 years, tens of millions of pilgrims stream to the small northern city of Allahabad from across India for the Maha Kumbh Mela, or Grand Pitcher Festival, at the point where the Ganges and Yamuna rivers meet with a third, mythical river.

Officials believe that over the next two months as many as 100 million people will pass through the temporary city that covers an area larger than Athens on a wide sandy river bank. That would make it larger even than previous festivals.

After a slow start, police chief Alok Sharma said 1.5 million people had gathered by 8 a.m. (0230 GMT) on Monday, with more on their way.