The Toynbee Tiles — someone paved Philadelphia's streets with manifestos and we never found them

Started noticing them in the 1980s, maybe earlier. Linoleum tiles embedded in asphalt in Philadelphia, New York, Boston, Kansas City. The original Philly ones are the longest-surviving. The tiles say things like TOYNBEE IDEA / IN KUBRICK'S 2001 / RESURRECT DEAD / ON PLANET JUPITER. Smaller tiles nea……