Mosaic is the art of creating images with an assemblage of small pieces of colored glass, stone, or other materials. It is a technique of decorative art or interior decoration. Most mosaics are made of small, flat, roughly square, pieces of stone or glass of different colors, known as tesserae; but some, especially floor mosaics, may also be made of small rounded pieces of stone, and called "pebble mosaics".Mosaic has a long history, starting in Mesopotamia in the 3rd millennium BC.