While I was in India, I attended the Kumbh Mela, a massive Hindu gathering on the holy Ganga river. In fact it is the largest human gathering on Earth. This year it's estimated that 40 million people had attended the Mela and bathed in the river between the beginning of the festival on January 14th, and the Royal Bath on April 14th. It's estimated that 10 million people bathed in the Ganga on April 14th alone.

The Kumbh Mela takes place every three years, in one of four cities, so that each city hosts the festival every 12 years. This is because, according to legend, Lord Vishnu spilt four drops of "the nectar of immortality" on Earth during a battle between the gods and demons. The four places where the drops fell are Prayag, Haridwar, Ujjain, and Nashik, all of which are on the Ganges river. This year the Kumbh Mela took place in the northern city Haridwar, where the Ganges comes out of the Himalaya - making it a place where the water is still relatively clean. It's believed that by bathing in the holy waters of the Ganges, a person is absolved of his sins, and the cycle of reincarnation is ended.

Normally Haridwar has a population of somewhere around half a million people, so you can imagine that it was incredibly crowded with 10+ million people there at once. There were tent cities sprawling in all directions around the city, and the city itself was filled with temporary camps, but it seemed very well organized. I suppose since it's been going on for so long, they've got it down pretty well at this point. Still, seven people died this year in a procession stampede.

I left Haridwar on April 13, the day before the Royal Bath and it was intensely crowded. It was difficult to even get a train ticket out on that day, and impossible to get one out after that, so I managed to get out of town just in time. All in all, it was a pretty incredible thing to witness.

A few interesting links:
Wikipedia entry
BBC Story with satellite photos
Official Kumbh Mela info site