A collective term for thunder stones or fossils believed by ancient people to be thunderbolts that fell from the sky.
From Greek 'keraunos' (thunderbolt) + '-ia' (condition, collection of). Ancient people called stone artifacts and fossils 'ceraunia' because they looked like objects that fell from storms.
Medieval Europeans hung ceraunia on their walls to ward off lightning strikes, not realizing these 'thunderstones' were actually fossils and ancient tools—but the superstition probably did protect buildings because the metal hooks used to hang them became natural lightning rods.
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