Street art
In 1999, an artist called Space Invader (who took his name from a video game) started putting little mosaic work in Paris. He started by doing it in a museum called the Louvre. French television showed it. Then he started doing it in every city he could. So he met other artists in other cities. Because his work is not ephemeral but very discreet, the authorities let him do. Only in Amsterdam, the city council decided to officially remove them.