An urban legend is a type of folklore, endlessly circulated by word of mouth, repeated in news stories and distributed by email. It is frequently recounted as having happened to a "friend of a friend". Some of the stories are very old, having been only slightly modified over the years, as in the story of a woman killed by spiders nesting in her elaborate hairdo. Others are new, as in the story of the man on a business trip being seduced by a woman and waking up the next morning with a kidney surgically removed for transplant.
Some urban legends are actually based on true events, such as the case of the young man shooting bullets into a large saguaro cactus. He was killed when his gunfire severed the trunk, resulting in his being crushed by the falling plant. Even when essentially true, however, the stories are often distorted by the many retellings from the original event.
The concept urban legend was first promoted by a professor of English, Jan Harold Brunvand, in his 1981 book The Vanishing Hitchhiker: American Urban Legends & Their Meanings. Brunvand used his collection of legends to make two points: first, that legends, myths, and folklore are not unique to so-called primitive or traditional societies, and second, that one could learn much about urban and modern culture by studying such legends. Brunvand has since published a series of similar books. Brunvand is also credited with first using the term vector (after the concept of a biological vector) to describe a person or entity that passes along an urban legend.
Discussing, tracking, and analyzing urban legends has become a popular pursuit. A thriving usenet newsgroup, news:alt.folklore.urban discusses such stories. The newsgroup's Frequently Asked Questions page summarises the truth or otherwise of these stories, so far as this can be determined. A similar list may be found on The Urban Legends Reference Page at snopes.com. For online urban legends, see Virus Myths and the Darwin Awards site, which also showcases a few stories each year of dubious veracity (they've promulgated Urban Legends as facts in the past). Finally the US Government Department of Energy has set up a service called Hoaxbusters that deals with all sorts of computer-distributed hoaxes and legends.
Certain early historians such as Tacitus, Geoffrey of Monmouth and Herodotus functioned as forerunners of urban myth, recycling hearsay and anecdotal accounts as historical facts; these writings, in turn served as the basis for other accounts, and thus many cycles of inaccurate historical narrative became self-perpetuating vicious circles. Contemporary historians tend to cast a very cold and careful eye over historical evidence emanating from writers such as these. For a list of these and other works considered to be suspect, see Dubious historical resources.
One classic urban legend claims the pope's crown or Papal Tiara contains the words Vicarius Filii Dei which when numerised adds up to 666, the number of the antichrist mentioned in the Bible. Though the story has no basis in fact (all papal crowns dating from the sixteenth century onwards are on public show and none contain the words), 'belief' in the 'myth' has continued, with constant specific references to an early twentieth century photograph at a papal funeral (probably Pope Leo XIII's in 1903) that proves the existence of a papal tiara with the words. Except that in one hundred years, no one has ever been able to produce the supposed photograph or even state definitively where it was supposedly published. Instead it is spoken of in terms of 'knowing someone who knows someone who definitively saw the photograph!', a phenomenon known in the Irish language as the 'Dhúirt bean liom gur dhúirt bean leí' syndrome (a woman told me that a woman told her that...)