Dr Richard Parkinson tells BBC News Online: "Nobody knew what the language of ancient Egypt sounded like"

It was known at the time to be an important find - but it was not until more than 20 years later that the Rosetta Stone's real significance became clear.

To celebrate its bicentenary the British Museum opens a new exhibition "Cracking Codes: The Rosetta Stone and Decipherment" on Saturday 10 July.

The Rosetta Stone, Ptolemaic, 196 BC

In 1822 the French scholar Jean-Francois Champollion managed to decipher the stone's Egyptian hieroglyphics - the first time hieroglyphics had ever been decoded.

Dr Richard Parkinson of the British Museum's Department of Antiquities says the stone is the museum most popular attraction.

"It was carved in 196 BC in two languages, Greek and Ancient Egyptian and it allowed people to read ancient Egyptian hieroglyphics for the first time in over 1,000 years.

It was the multicultural nature of Egyptian society that led to the stone being inscribed in two different languages. But despite this cracking the code on the stone was a "hideously complicated affair" according to Dr Parkinson.

A reconstruction of what the original stone would have looked like

"What you have is two different scripts and you also have two different languages - and of course nobody knew what the language of ancient Egypt sounded like."

But when it was cracked the subject of the text was "one of the great disappointments" according the Dr Parkinson.

"Everyone was expecting the hieroglyphics to be mystical symbolic pictures, whereas in actual fact they are fairly efficient, fairly normal writing system."

The stone is actually a decree issued by the priests of Egypt in favour of the Greek born King Of Egypt Ptolemy and among other things details rather mundane tax concessions.

It is now the centrepiece of the Museum's new exhibition.

A red sandstone sphinx with inscriptions in Egyptian hieroglyphics

Dr Parkinson says: "What we are trying to do is show the Rosetta Stone in radical new light. We've had it properly cleaned so absolutely every detail is legible now. We are trying to show the full impact it had on our knowledge of ancient Egypt."

The Rosetta Stone helped to unlock Egyptian culture and not only for those in the academic world.

The cinema has long loved a good epic and the 1955 Hollywood film The Egyptian was based on an ancient Egyptian poem. Currently the movie blockbuster The Mummy is attracting large audiences.

Perhaps surprisingly Dr Parkinson is a fan too. He says he thinks The Mummy is "good fun".

"It's not outstandingly accurate in details, but I've really got to approve of the fact that it makes the ability to read hieroglyphics of crucial importance. I think from that point of view the plot is very good."