Very Interesting to see that a majority of the mega huge gatherings have occured in India. These stats are courtesy Wikipedia.
In January 2001, a reported 70 million Hindu pilgrims from around the world travelled to Hindu holy city of Prayaga (also known as Allahabad) in India for the Kumbh Mela, the world’s largest religious festival and also the world’s largest gathering.[1][2]
In April 2004, Around 30 million Hindu pilgrims from all over the world travelled to Hindu holy city of Ujjain in India for the Simhastha Kumbh Mela.[3]
The funeral of C. N. Annadurai, a former Chief Minister of the Indian state of Tamil Nadu, was attended by an estimated crowd of 15 million people.[1]
