If one Italian scientist is correct then the telescope was not invented sometime in the 16th century by Dutch spectacle makers, but by ancient Assyrian astronomers nearly three thousand years earlier.

BBC News' Dominic Hughes: This could mean that the telescope was invented two and a half thousand years earlier

According to Professor Giovanni Pettinato of the University of Rome, a rock crystal lens, currently on show in the British museum, could rewrite the history of science. He believes that it could explain why the ancient Assyrians knew so much about astronomy.

But experts on Assyrian archaeology are unconvinced. They say that the lens is of such low quality that it would have been a poor aid to vision.

Magnifying glass

It is called the Nimrud lens and it was found in 1850 by the legendary archaeologist Sir John Layard, during an epic series of excavations at the palace of Nimrud in what is now Iraq.

Trinket or telescope?

Upon his return to England, he showed the lens to physicist Sir David Brewer who thought it could have been used as a magnifying glass or to concentrate the Sun's rays.

Used as a magnifying glass, it could have been useful to Assyrian craftsman who often made intricate seals and produced minuscule texts on clay tablets using a wedge-shaped script.

It is a theory many scientists might be prepared to accept, but the idea that the rock crystal was part of a telescope is something else. To get from a lens to a telescope, they say, is an enormous leap.

Saturn's serpents

Professor Pettinato counters by asking for an explanation of how the ancient Assyrians regarded the planet Saturn as a god surrounded by a ring of serpents?

Could they not have seen Saturn's rings through their telescope and interpreted them as serpents? An unconvincing argument, say experts. The Assyrians saw serpents everywhere. And why is it in their many astronomical reports on clay tablets there is no mention of such a device?

The conventional understanding of the invention of the telescope is that it was developed in the 16th century by Dutch spectacle-makers who held one lens in front of another.

One thing is sure: Galileo did not invent it - a common misconception - although he was one of the first to turn it towards the sky. By then, lenses used as spectacles had been known for hundreds of years at least, and it has been a puzzle to historians why it took so long for the telescope to be invented.

Commercial and military use

It may have been developed and then forgotten, or even kept secret. However, experts regard this as unlikely given the commercial and military uses that a telescope could serve.

Galileo did not invent the telescope

Whatever its origin, as ornament, as magnifying lens or part of a telescope, the Nimrud lens is the oldest lens in the world. Looking at it evokes mystery and wonder. It can be seen in room 55 of the British Museum, in case 9 of the Lower Mesopotamian Gallery

It may not be unique. Another, possibly 5th century BC, lens was found in a sacred cave on Mount Ida on Crete. It was more powerful and of far better quality than the Nimrud lens.

Also, Roman writers Pliny and Seneca refer to a lens used by an engraver in Pompeii. So perhaps the ancients knew more about lenses than we give them credit for.