In 1835 Sir Henry Rawlinson investigated some writings and figures carved in a stone wall on the road between the ancient capital of Babylonia and Media, located in modern Iraq . The writings were on a panel carved into the rock, the panel being 15 meters high and 25 meters long. The panel is 100 meters above the foot of the cliff.
Using copies of the text that he made, Rawlinson determined that the text of the inscription was a declaration, geneology, and history lesson written by King Darius of Persia, written before his death in 486 BC. The inscription was important because the same message is written three major languages of the day: Old Persian,Elamite, and Babylonian. Like the Rosetta stone, the fact that when one of these message could be deciphered, that meant the other two messages could be deciphered.
About one third of the Old Persian alphabet were known, and Rawlinson figured out the rest, aided by the fact that the ancient language had similarities to the modern Persian of the region. Once the words in Old Persian were known, translating the same words in the other two languages came fairly fast. Thus was learned how to read these old languages.
When the text was finished, Darius had the access trails to the rock panel cut away, which helped preserve the inscription to modern times.