Then, in 1798, Britain and France went to war, and fought in Egypt. Napoleon, the French general, took a big term of scholars with him to study the monuments. But it was his soldiers who made the most important discovery – a slab of black stone, near the Mediterranean sea, at a place called Rosetta. It had three different scripts on it – one Greek, and two Egyptian. The French scholars guessed the the texts were translations of each other.
The Rosetta Stone, as it became known, did indeed make it possible to decipher hieroglyphs. Most of the work was done by a Frenchman, Jean-François Champollion, and an Englishman, Thomas Young.
Source: The Usbourne Encyclopedia of Ancient Egypt