Kumbh Fair, Haridwar
The religious aspect and the legends of Kumbh Mela remains associated to very old date back to the time when Kalasha (pot of nectar for immortality) was recovered from the churning of premodial ocean for which a tensed war between God and Demon ensued.
As per Hindu mythology and history, Lord Bharma - God of creation gave some advise to the gods to get rid of their weakness, caused during the creation of earth. Following the advise of Lord Brahma, the god began the task of churning od ocean in order to achieve nectar (Amrit) from its water. As the task was very tough, God sought assistance of demons and made a deal with demon that they could have latter half of the nectar that was to be obtained from churning of Ocean.
The first ever written evidence of Kumbh Mela could be accounted to Chinese Traveler, Huan Tsang or Xuanzang dated 602 - 664 A.D. However, the observance dates back many centuries to ancient India's Vedic period, where the river festivals first started getting organised.
The account goes that the Gods had lost their strength, and to regain it, they thought of churning the Ksheera Sagara (primordial ocean of milk) for amrita (the nectar of immortality). This required them to make a temporary agreement with their arch enemies, the demons or Asuras, to work together with a promise of sharing the nectar equally thereafter. However, when the Kumbha (urn) containing the amrita appeared, a fight ensued. For twelve days and twelve nights (equivalent to twelve human years) the gods and demons fought in the sky for the pot of amrita. It is believed that during the battle, Lord Vishnu flew away with the Kumbha of elixir spilling drops of amrita at four places: Allahabad, Haridwar, Ujjain and Nashik.
Ardh Kumbh Mela is celebrated after every six years, and Maha Kumbh is celebrated every 12 years at Haridwar. Last Maha Kumbh was held in Haridwar in year 2010.