It was the world's first empire: three quarters the size of the US, it built the forerunner of the Suez channel and wrote what some call the earliest "bill of human rights". And now, 2,500 years later, the glory of ancient Persia can be seen at the British Museum.

The first exhibition ever on the forgotten kingdom brings together material from three countries, some never before seen in public.

Cyrus the Great founded the empire in 550 BC when he united the Medes and the Persians. More conquests followed, creating the world's largest kingdom until then.

At its height, it covered 7,500,000 square miles - from Libya in North Africa to the River Indus in modern Pakistan. It lasted for 200 years, until Alexander the Great burnt its capital, Persepolis, to the ground in 330 BC.

Seven storey columns

The exhibition highlights the scale and splendour of the ancient city with recreations, including a column from the Hollywood film Alexander. It is a small-scale version of the 72 massive columns that held up the roof of the Apadana, or meeting hall, which could house 10,000 people at Persepolis.

Soaring nearly seven storeys into the air, they were the tallest and thinnest columns mastered at the time. After almost 2,500 years, only 14 of them tower above the ruins in the arid landscape of south-west Iran.

Plaster casts of 23 stone reliefs that lined the two giant staircases leading up to the Apadana are also on display. Made by a British Museum expedition more than a century ago, the casts contain detail that has since weathered away on the originals.

The panels, hidden away in museum's warehouses until now, were combined with objects from the Louvre, Paris, and two museums in Iran to create the exhibition.

Another set of relief panels, from the Louvre, portray the king's 10,000 bodyguards. If a guard died, he was replaced immediately earning them the name "The Immortals".

'First empire'

Persia is often called the "first empire", said curator John Curtis. Unlike their Babylonian predecessors, who focused on looting, the Persian kings administrated the many nations under their control.

About 20 satraps ruled the provinces of groups such as Egyptians, Greeks, Indians and Babylonians.

A 1,600-mile-long royal road was built from Sardis, in what is now Greece, to Susa, in south-west Iran.

King Darius also constructed a waterway between the Nile and the Red Sea a precursor to the Suez channel.

Religious tolerance

The Persian kings worshipped the Zoroastrian god Ahura Mazda, but did not follow the religion's practice of laying bodies on towers of silence to be picked clean by birds of prey.

Instead, they buried their dead - sometimes in bronze coffins shapes like bath tubs. One such coffin, found at Susa with a treasure trove of jewellery among the remains, was reconstructed for the exhibition.

Whatever their beliefs, the Persians showed much more religious tolerance than the Babylonians before them.

The famous Cyrus Cylinder, a barrel-shaped stone buried in the foundations of Babylon after Cyrus conquered it, is proof of this.

An inscription on it contains an order of the king that permitted cults to worship their own gods. People taken captive by the Babylonians should also be sent home, it adds.

Although the text does not mention the Jews, experts believe it was at that time when they were allowed to return to Jerusalem to rebuild the temple.

Yet despite its rich heritage, the Persian empire is largely forgotten in the west, Mr Curtis said.

The curator hopes the exhibition will change this.

"It may also be important in this time of difficult east-west relations to remind people in the west of a remarkable cultural legacy of a country like Iran."

  • Forgotten Empire: The World of Ancient Persia, now open, will run at the British Museum until January 8, 2006. Entry £8.