Imagine a crowd so massive, it is visible from space. A crowd, likely 100 million strong intent on just one thing: bathing in a sacred river to wash away sins and gain a chance at a new beginning.

Once every 12 years, Hindus from around the world converge at Sangam in Allahabad, India, at the convergence of the Ganges, Yamuna and the mythical Saraswati rivers. It is known as the Maha Kumbh Mela, and it is not only the world’s largest religious festival, it is also believed to be the largest gathering of humans in one place, at one time on earth. The festival began on January 14 and lasts through March 10.

The Kumbh Mela is a mass gathering of Hindus from across India and around the world in a place where the Ganges, Yamuna and mythical Saraswati rivers converge in Allahabad, India, called the sangam.

Astrology determines most aspects of the festival, including its exact date and length. Where the festival is held also depends on the position of Jupiter, the sun and moon.

This year, the Maha Kumbh Mela will last 55 days, starting on January 14th and ending on March 10th. The festival has been held on the banks of the Ganges for thousands of years. There are different kinds of kumbh: an ardh (or half) kumbh is held every six years at two set locations; a purna (full) kumbh is held at Allahabad every 12 years. A Maha Kumbh Mela happens once every 144 years.

The Kumbh Mela is held at Haridwar, Ujjain and Nasik every three years but the Kumbh at Allahabad has a special significance, where it is held at Sangam, the confluence of the rivers Ganga-Yamuna and the mythical Saraswati.The official site for Kumbh Mela says “The Prayag (Allahabad) Kumbh Mela is the largest and holiest of all melas and is believed to be the most auspicious” More than 100 million people are expected to attend the 55-day festival in 2013. In 2001, nearly 70 million flocked to the Ganges’ shores of the Ganges for the Purna Kumbh Mela.

The origin of the Kumbh Mela religious festival comes from a legend describing a war between gods and demons over possession of the elixir of eternal life or the “nectar of immortality.”According to the legend the “kumbh” was the container that held “the immortal nectar” of the gods. It is believed that a few drops of this elixir fell to earth at four places during various times of these battles. These four places are where the rivers are believed to possess mystical powers. Because the gods and demons battled back and forth for twelve days and twelve “days” for the gods are equivalent to 12 years for humans, the Kumbh Mela is celebrated once every 12 years in each of these four places – Haridwar, Ujjain, Nasik and Allahabad.

Cleffairy: Don’t forget to watch the premiere of World’s Biggest Festival: Kumbh Mela on 2 March 2013 at 10.00pm exclusively on National Geographic Channel (Astro Ch 553)