Simhastha is the great bathing festival of Ujjain. It is celebrated in a cycle of twelve years when Jupiter enters the Leo sign of the zodiac, known as Simha Rashi. Ceremonial bathing in the holy waters of Kshipra begins with the full moon day of Chaitra month and continues throughout the succeeding month of Vaishakh culminating on tenth full moon day.
Tradition calls for ten different factors to be located for the grand festival at Ujjain. According to the Puranas, the legendary churning of the ocean by the gods (Devas) and demons (Danavas) yielded, amongst other things, a jar (Kumbha) full of nectar (Amrita). Gods did not like to share it with demons. At the instance of Indra, his son Jayanta tried to run away with the jar and was followed by some of the demons. During the struggle for its possession lasting over twelve days in heaven, a few drops of the nectar dropped at the four places, corresponding with Haridwar, Prayag, Ujjain and Nasik on the earth. The drops of nectar were received by the holy rivers at these places. The struggle for the possession of the nectar-jar (Amrita-Kumbha) lasted for twelve days in heaven, the equivalent time being twelve years on the earth.
The festival at the other three places is known by the popular name Kumbha. The cycle of twelve years is common to all the four places. Different planetary positions, like the crossing of Jupiter into Leo sign and certain other conjunctions for the fair at Ujjain, are noted for the kumbha-fair at these other places also. Besides being a city of remarkable cultural traditions, Ujjain is cited among the seven cities of sacred merit in India