Decree of Canopus, ancient bilingual, trigraphic Egyptian decree that provided a key for deciphering hieroglyphic and demotic scripts. The decree, written in Greek, demotic, and hieroglyphs, was promulgated March 7, 238 bce, by an assemblage of priests upon the death of a daughter (Berenice) of Ptolemy III Euergetes and his consort, Berenice; it honours the girl as a goddess. The two copies of the decree discovered at Tanis (modern Ṣān al-Ḥajar al-Qiblīyah) in 1866 are considered by many scholars to be second only to the Rosetta Stone in their value for deciphering ancient Egyptian. Three fragmentary copies have also been found.