The Rosetta Stone is a granitoid slab inscribed in hieroglyphic, demotic, and Greek with identical texts of a decree by a council of priests during the reign of Ptolemy V. Part of a stele dating from 196 B.C., it was found (1799) by Napoleon's troops near the city, was taken (1801) by the British, and since 1802 has been displayed at the British Museum. It gave Jean-François Champollion, Thomas Young, and others the key to Egyptian hieroglyphic.
See study by R. B. Parkinson (1999).