During excavations of the ancient Assyrian capital of Kalkhu (better known as Nimrud, in Iraq) in 1850, archaeologist Austen Henry Layard found a piece of rock crystal buried under the ruins of the Northwest Palace's throne room.
It was under other pieces of glass that seemed to have been part of an object, perhaps wood or ivory, that had broken or disintegrated over the centuries.
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With the glass bowls a rock crystal lens was discovered, with opposite flat and convex faces. The Assyrians did not know its characteristics, so it is the first example of magnifying glass and glass to burn. It was buried under a heap of fragments of beautiful opaque blue glass, apparently the enamel of some ivory or wooden object, which had perished.
—Austen Henry Layard, Discoveries in the Ruins of Nineveh and Babylon
Nimrud lens. Photo: The British Museum