The following
description comes from page 431 of The Lonely Planet's guide to India
(7th edition, November 1997):
"According
to Hindu creation myths, the gods and demons once fought a great battle
for a kumbh (pitcher) containing the nectar of immortality.
Vishnu got his hands on the container and spirited it away, but during
his flight four drops of nectar spilt on the earth - at Allahabad,
Haridwar, Nasik and Ujjain. The fight lasted 12 days but the
gods finally triumphed and got to quaff the nectar - a scene often
portrayed in illustrations of Hindu mythology.
A huge
mela (fair) is held at each of the four places the sacred nectar
fell once every 12 years (since one day in the life of the gods equates
to 12 years in the life of mortals). It is due to take place
in Haridwar in 1998 and then in Allahabad in 2001. The Allahabad
Kumbh Mela is the largest and holiest mela of them all - some say
the largest religious gathering that takes place anywhere on earth.
Unsubstantiated estimates of the numbers who came to bathe in the
Ganges and Yamuna during Allahabad's last Kumbh Mela in 1989 ran as
high as 20 million, though it was probably lower than this.
The event is noted for the huge number of Hindu holy men it attracts,
especially the naked sadhus or nagas of militant Hindu monastic
orders.
Mark
Tully's No Full Stops in India has a fascinating chapter on
the politics, logistics and significance of Allahabad's last Kumbh
Mela."