This is often in the event the nagas grew to become much too populous and started to torment the people. This is often every time they ended up cursed by their grandfather, Lord Brahma, with annihilation. The nagas begged for mercy but had been sent to Patala, the underworld. https://franciscogvhte.bloggazza.com/35003816/the-smart-trick-of-23naga-that-nobody-is-discussing