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.'