Nimrud lens or Layard lens is a 3000-year old piece of rock crystal, which was unearthed at the Assyrian palace of Nimrud, Iraq.
Nimrud lens is slightly oval, and was roughly ground, perhaps on a lapidary wheel. It has a focal point about 11 centimetres (4.5 in) from the flat side, and a focal length of about 12 cm. It would be equivalent to a 3X magnifying glass.
Assyrians must have used it as a magnifying glass, or as a burning-glass to start fires by concentrating sunlight, or it may have been a piece of decorative inlay.
Surface of the lens has twelve cavities that were opened during grinding, which would have contained naptha or some other fluid trapped in the raw crystal.
Few scientists have proposed that the nimrud lens was used by the ancient Assyrians as part of a telescope, which explains their knowledge of astronomy.
But this theory was rejected by many other scientists as the optical quality of this lens does not appear to be sufficient to view distant planets.
The theory of nimrud lens being a telescopic lens emerged from the thought that, ancient assyrians saw the planet Saturn as a god surrounded by a ring of serpents, which was their interpretation of Saturn’s rings as seen through a low quality telescope.
Nimrud lens was found buried beneath other pieces of glass which looked like the enamel of an object, perhaps made of wood or ivory, which had disintegrated.
Presently, it can be seen in room 55 of the British Museum, in case 9 of the Lower Mesopotamian Gallery
One thing is sure : Galileo did not invent first telescope.
Another lens, possibly from 5th century BC, was found in a sacred cave on Mount Ida on Crete. It was more powerful and of far better quality than the Nimrud lens.
Roman writers Pliny and Seneca refer to a lens used by an engraver in Pompeii.
So, much prior to Galelio, telescopes were invented and used in many ancient civilizations, but were not made popular.