If you've never heard of the Kumbh Mela, well, you're sort of forgiven. As Quartz explains, the event is largely ignored by the West—even though it occurs every three years, with a big to-do every 12, and just so happens to be the "largest human gathering in history." This is one of those purna ("complete") years, and attendance estimates for the 55-day religious festival, which began this week, top out at 110 million Hindus. They'll gather at the Sangam, the confluence of the Ganges, the Yamuna, and the mythical Saraswati, to wash away their sins; more than 10 million were expected to do so on the first day alone. Some of the numbers behind the gathering, per the AP and BBC: