The Nimrud lens is a 3,000-year-old piece of rock crystal unearthed by Sir John Layard in 1850 at the Assyrian palace of Nimrud, in modern-day Iraq. Since its discovery over a century ago, scientists and historians have debated its use, with one prominent Italian professor claiming the lens was used by the ancient Assyrians as part of a telescope. This was used to explain how the Assyrians knew so much about astronomy.

The Nimrud lens (also called the Layard lens), which has been dated to between 750 and 710 BC, is made from natural rock crystal and is a slightly oval in shape. It was roughly ground, perhaps on a lapidary wheel. It has a focal point about 11 centimeters (4.33 in) from the flat side, and a focal length of about 12 cm (4.72 in).

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These dimensions would make the Nimrud lens equivalent to a 3× magnifying glass. Combined with another lens, it could achieve much greater magnification. The surface of the lens was created with twelve cavities that were opened during grinding. These would have contained naptha or some other fluid trapped in the raw crystal. The lens is said to be able to focus sunlight, although the focus is far from perfect.

Read more: Ancient Origins