"Mr Avery said it was written on the Rosetta Stone"
The Rosetta Stone is a large black basalt slab bearing an inscription dating from the year 196 BC. It was the crucial key to deciphering Egyptian hieroglyphs, and the foundation of modern Egyptology. The Egyptian hieroglyphics on the stone are accompanied by a Greek translation, as well as one in Demotic (a form of Egyptian). As scholars were able to read the Greek, they could use it to decipher the Egyptian.

The inscription concerns the priests and the King of Egypt. It was a decree passed by a general council of priests on the first anniversary of the coronation of Ptolemy V Epiphanes - the 13 year old King of Egypt. The text concerns the honours bestowed on the king by the temples of Egypt in return for services rendered by him, both at home and abroad. Priestly privileges, particularly those of an economic nature, are listed in detail.

See more about the Rosetta Stone here.