The Maha Kumbh Mela ("great festival of the pot of nectar of immortality") is held every three years in each of four different locations, returning to each of four places every twelve years. An Ardh (half) Mela (festival) takes place six years after the Maha Kumbh in each location.
Holy Bath. Prayag. Ardh Kumbh Mela 2007
Pilgrims bathing during the main bath in Prayag. Still night, 3:13 AM but thousands of pilgrims are flocking to the Ganges