The Rosetta Stone is a granodiorite stele inscribed with a decree issued in Memphis on behalf of King Ptolemy V in 196 BCE. It was discovered by a soldier, Pierre-François Bouchard, during Napoleon Bonaparte's expedition to Egypt. The text was deciphered by Jean-François Champollion, which provided the key to understanding Egyptian hieroglyphics.
Somehow, the Templars procured a rubbed transfer of the missing section of the Rosetta Stone. Champollion, an ally of the Assassin Brotherhood, discovered that the rubbing contained sensitive information concerning the Assassins, which prompted the Assassin Council to task Arno Dorian with recovering its pieces, with Champollion's aid.