The Visby lenses are ten lens-shaped rock crystals found in a viking grave in Gotland dating from the 10th century. Some of them are mounted in silver and may have been carried as a pendant, but others appear not to have been used as jewelry. The lenses are almost perfectly elliptical and very similar to modern lenses. They may have been used for magnification, to start fire or in a telescope. 5 April, 2000, BBC News: Did the Vikings make a telescope? The visby lenses. Schmidt O, Wilms KH, Lingelbach B. Aalen University of Applied Science, Germany.

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