The Rosetta Stone was found by Napoleon’s soldiers in Egypt in 1799. It was read by Jean-François Champollion in 1822, and thus became the key to unlock Egyptian hieroglyphics. The Rosetta Stone is now displayed in the British Museum in London, where it has been since 1802.
Candace Keener writes the story of the Rosetta Stone in HowStuffWorks here.
HT: Jack Sasson