Apep (Apophis) is the great serpent of chaos who dwells in the primordial waters and tries every night to devour the sun god Ra as Ra travels through the Duat (the underworld) [S2][S4]. At the hour of the sun's weakest point (around midnight), Apep strikes; the sun god (helped by Thoth and others) defeats him — often with a knife or by the 'Eye of Ra' (Sekhmet) [S2][S4]. The defeat is repeated nightly: Apep is not permanently destroyed, he is merely driven back. This nightly battle is the mythic basis for the Egyptian understanding of the sun's daily rising [S2][S4]. Priests performed rites each night to 'bind' Apep [S4].