Abilingual decree of 196 BC built into the fort at Rosetta discovered by the French during reconstruction work in 1797. The same decree is written in the hieroglyphic, demotic, and Greek scripts. The importance of these texts for the decipherment of the Egyptian scripts was immediately realized, and copies were sent to Paris, where the stone was to be shipped. Following the surrender of French forces in 1801, however, the Rosetta Stone was given, with Turkish approval, to the British by the Treaty of Alexandria and assigned to the British Museum in 1802. Decipherment of the hieroglyphic writing proved difficult and centered on the royal names in cartouches. The major breakthrough was made by Jean-Francois Champollion in 1822, when he recognized the alphabetic and ideogrammatic nature of the hieroglyphic text. The Rosetta Stone has become the symbol of the key that unlocks mysteries.
See also Young, Thomas.
Historical Dictionary Of Ancient Egypt by Morris L. Bierbrier
Ancient Egypt. A Reference Guide. EdwART. 2011.