The Toynbee tiles (also called Toynbee plaques) are messages of mysterious origin found embedded in asphalt of streets in about two dozen major cities in the United States and four South American capitals. Since the 1980s, several hundred tiles have been discovered. They are generally about the size of an American license plate (roughly 30cm by 15 cm), but sometimes considerably larger. They contain some variation on the following inscription:
IN MOViE `2001
ON PLANET JUPITER.
Some of the more elaborate tiles also feature cryptic political statements or exhort readers to create and install similar tiles of their own. The material used for making the tiles was long a mystery, but evidence has emerged that they may be primarily made of layers of linoleum and asphalt crack-filling compound.