The Rosetta Stone unlocked the key to ancient Egyptian language of Hieroglyphics, which is a picture language, with one symbol for each word.
It contains a decree giving honours to Ptolemy V Epiphanes from 200 BC because he showed favour to the priests and temples. It was discovered in 1799 in Rosetta, a town in the western part of the Nile delta in Egypt, by Lt. Bouchard in Napoleon's army. It was surrendered to the British after the defeat of the French.
It has three Panels:
Bottom: Greek (capital letters). The last paragraph stated that all three texts carried the same message.
Top: Egyptian hieroglyphics script
Middle: Another unknown script
A British physicist, Young, noted that six names of royalty appeared in the Greek text, both kings and queens.
Champolion, a French genius, at the age of 11 dedicated his life to deciphering the hieroglyphics. At the age of 16, he showed that the Coptic language, which is still in use today, preserved the ancient Egyptian language, called Demotic, a simpler form of writing from 800 BC, much nearer our alphabetic writing, which was the previously unknown third language on the middle of the stone. In 1822 he deciphered the hieroglyphics by noticing that the names in oval lines (cartouches) read "Ptolemy & Cleopatra".
Being able to read Egyptian hieroglyphics gave an immediate perspective of history, from 2000 years ago, right back to 5000 years ago. This disproved the idea that the Greeks invented writing around 700 BC.