Western European traditions, including English, Scandinavian and Celtic, claimed that fairy rings are the result of elves or fairies dancing. Such ideas dated to at least the mediæval period; The Middle English term "elferingewort" ("elf-ring"), meaning "a ring of daisies caused by elves' dancing" dates to the 12th century. In his "History of the Goths" (1628), Swedish writer Olaus Magnus makes this connection, saying that fairy rings are burned into the ground by the dancing of elves. British folklorist Thomas Keightley noted that in Scandinavia in the early 19th century, beliefs persisted that fairy rings ("elfdans") arose from the dancing of elves. Keightley warned that while entering an "elfdans" might allow the interloper to see the elves—although this was not guaranteed—it would also put the intruder in thrall to their illusions.