POLITICAL PILGRIMAGE
This year's event comes at a critical time for Modi's Hindu nationalist Bharatiya Janata Party (BJP), expected to face a tough contest in a general election due to be held by May.
It lost power in three key states in assembly elections in December, and will want to avoid a similar result during the general election in Uttar Pradesh, a state of 220 million where a good showing can often decide the contest.
The state's chief minister, Yogi Adityanath, is a firebrand Hindu monk from the BJP, who has championed policies that play to the party's core Hindu base.
This year Adityanath has transformed a smaller Ardh, or "half" Kumbh Mela, into a full version of the festival.
He has also lobbied for a controversial Hindu temple on the site of a former mosque, and renamed several cities - including Prayagraj, which used to be known as Allahabad until it got its new name in October.
Modi and his rival, opposition Congress leader Rahul Gandhi, are both expected to attend the festival before it wraps up in March.
