“The Rosetta Stone is a fragment of an Ancient Egyptian granodiorite stele whose engraved text provided the key to the modern understanding of Egyptian hieroglyphs. The inscription records a decree that was issued at Memphis in 196 BC on behalf of King Ptolemy V. The decree appears in three texts: the upper one is in ancient Egyptian hieroglyphs, the middle one in Egyptian demotic script, and the lower text in ancient Greek.”
This fascinated me when I was a child. What a remarkable find! Read the rest of the story at Wikipedia.