Ancient Chinese cosmology divided the sky into nine layered heavens, with
九天 being the topmost. It contrasts with
九地 (jiǔdì, the deepest underground). Li Bai's poem
《望庐山瀑布》 contains the famous line
飞流直下三千尺，
疑是银河落九天 - 'The torrent plummets three thousand feet, as if the Milky Way is falling from the ninth heaven.'
