Yesterday, July 19, marks the anniversary of the discovery of the Rosetta Stone in 1799! (I'm currently reading Discovery at Rosetta by Jonathan Downs). It was a very (maybe the) important discovery in archaeology because it was the first clue to deciphering Egyptian hieroglyphs, which up until then had been a complete mystery. The Stone is fragment of a Ptolemaic-era stele with an inscription recording a decree made in Memphis in 196 BC which appears in 3 versions--one in hieroglyphs, one in the Egyptian demotic script, and one in ancient Greek. It was displayed in a temple for everyone to see, and later buried and then used as building material in a fort.
It remained there, unnoticed, until Napoleon's campaign to Egypt in 1798, when he was accompanied by a group called the Commision des Sciences et des Arts, 167 scientists and artists who wanted to study ancient Egyptian culture. In July 1799 soldiers were sent to reinforce Fort Julien, a couple miles northeast of the port city Rashid, and while there Lieutenant Pierre-Francois Bouchard spotted a slab with inscriptions on one side and it was sent to the Commision for a look. The three different inscriptions were rightly suspected that it could be versions of the same text. The Stone was seized by the British in 1801 when they defeated what was left of the French forces in Egypt after the departure of Napoleon. It has been displayed at the British Museum since June 1802.
For more info, this is a great site!