The Rosetta Stone, which dates back to 196 BC, is one of the British Museum's most treasured exhibits – and is a broken piece of a bigger stone slab.
Carved into it is a decree about the king, Ptolemy V, written three times in three different scripts – hieroglyphs, Ancient Greek and Demotic, a native Egyptian script.
At the time of its discovery, no-one understood how to read ancient Egyptian hieroglyphs.
It was found by accident by Napolean Bonaparte's Army as they were digging in the foundations of the Rashid (Rosetta) at the Nile Delta in July 1799. It had apparently been built into a very old wall.
The officer in charge, Pierre-François Bouchard, realized the importance of the discovery.
But after Napoleon's defeat, the stone was handed over to Britain under the terms of the Treaty of Alexandria in 1801 along with other antiquities the French found.
It was shipped to England and arrived at Portsmouth in February 1802 and was presented to the British Museum by King George III in July.
At first, the Rosetta Stone and other sculptures were placed in temporary structures at the museum's grounds because the floors were not strong enough to take their weight.
The Rosetta Stone has been on display at the British Museum (pictured) since 1802
After a plea to Parliament for funds, construction began in a new gallery to house the acquisitions.
It has been on display since 1802 with only one break towards the end of the First World War.
The museum was concerned about heavy bombing in London in 1917 and the stone was moved to safety along with other important objects.
It lays the next two years in a station on the Postal Tube Railway 50 feet below the ground at Holborn.
In the early years of the 19th century, scholars used the Greek inscription on the Rosetta stone to crack the code of the hieroglyphs.
Thomas Young, an English physicist, What the first to show that some of the hieroglyphs on the Rosetta Stone wrote the sounds of a royal name: Ptolemy.
French scholar Jean-François Champollion then realized that hieroglyphs recorded the sound of the Egyptian language.
Champollion made a crucial step in understanding ancient Egyptian writing when he pieced together the alphabet of hieroglyphs used to write the names of non-Egyptian rulers.
He announced his discovery in a paper at the Academy of Inscriptions et Belles Lettres at Paris in September 1822.
Champollion made a second crucial breakthrough in 1824, which did not apply for foreign names, but also for the Egyptian language and names.
Source: British Museum