A mosaic is a piece of decoration made from tiny fragments of material. The most common materials are pieces of stone, glazed (glass-coated) pottery and coloured glass. Pieces of shell and ivory have also been used. Mosaics can be designed to make pictures, in which case a variety of tiny square stones of different colours are needed. If the design is meant just to be a piece of colourful art, then any kind of size can be used.

First the pattern for the mosaic is drawn out on to the ground to act as a guide. The small stones are thick blocks. The thickness is needed to stop the stones moving about when pressed. The stones are set in a bed of cement. When it has all set, cement will be brushed over the stones so that it fills in all the gaps. It will then be wiped off with a wet cloth so that the stones are not stained by the cement.

The idea of making ‘paintings’ of recognisable scenes using coloured stones dates back to the times of Ancient Greece and Ancient Rome. The themes used by the Ancient Greeks and Ancient Romans were scenes from their myths and often featured gods, although some showed feasts and contests between gladiators. The themes often suited the place where they were made. For example, in the Roman port of Ostia, the mosaics in the baths are of Poseidon, the god of the sea (see video below). Mosaics also featured famous battles, such as the Alexander Mosaic in Roman Pompeii, made about 100BC and which shows a scene of a battle between the famous Greek king Alexander the Great and Darius, the king of the Persians.