The curious case of the Toynebee Tiles and their continuing legacyThe most culturally revered street art is often wrapped in an element of intrigue: Banksy's quasi-anonymity has garnered as much attention as his artwork. But what happens when that intrigue swells far beyond the bounds of mere mystery and consumes the very message of the art?The biggest guerrilla art movement of our time is older than Banksy, more geographically promiscuous than JR, and has remained unsolved for nearly three decades. Known as the Toynbee Tiles, they are plaques embedded in asphalt, usually at major intersections and pedestrian crosswalks, each containing a variation of the inscription: Though many attribute the original tiles to the social worker James Morasco, that theory doesn't quite add up. Not only does his widow firmly deny he had anything to do with the tiles, but new tiles have continued to emerge in the years after his death in 2003. The newer ones vary on the inscription to read:

TOYNBEE IDEAMOVIE 2001RAISE DEADPLANET JUPITERIn 2005, Philadelphia artist and researcher Justin Duerr began working on a documentary about the mystery. The film is yet to be released and its website has been stagnant since 2006, but it led some to surmise that the newer tiles featuring the word "movie" were laid by the filmmakers in an attempt to pique interest in their project. (In an NPR interview, Duerr denied this and attributed the tiles to a copy-cat.)But even if the newer tiles were a guerrilla marketing campaign, it still begs the question of who laid the tiles between 2003, when Morasco died, and 2005, when work on the film began. If we believe Morasco did lay most of the tiles, he would have been in his seventies when the bulk of them were deployed. Was he, on a social-worker's salary, really hopping around to over two dozen cities laying tiles that late in his life?What makes this mystery so fascinating is that, unlike traditional street art, it no longer embodies a clear social or political statement by a single author. Instead, it has taken on a life of its own, one in which the medium has truly become the message-these plaques continue replicating, driven, presumably, by several people acting without a real understanding of what the original message was. Indeed, the Toynbee Tiles mystery thrives on its own, inspiring speculation, intrigue and interpretation to this day, which may have been the creator's original intention after all.And in a way, though not on Jupiter, he-or she-has been resurrected.Guest blogger Maria Popova is the editor of Brain Pickings, a curated inventory of miscellaneous interestingness. She writes for Wired U.K. and spends a shameful amount of time on Twitter. Photos by Eric Haag.