The first examples of decorative mosaics were found in a temple in modern-day Iraq and dated from 3000 BCE. Since that time, civilisations across the world have used mosaics. Romans named individual tiles ‘tesserae’, which were small pieces of stone, beads or any material that could be arranged to form an image.
Colours were achieved using carefully selected stone or shell and, for more elaborate examples, coloured glass and stone coated in gold leaf. In floor mosaics, a ground layer called statumen was packed with small pebbles onto which 25 centimetres (ten inches) of mortar called rudus was poured.
A finer-grade rudus, known as nucleus, was poured on top of that and the design was etched into the surface, before the tesserae were set in place. Mosaics were applied using one of three techniques: direct application to the surface for 3D objects; indirect application to a backing, before being transferred to a surface; or double indirect, a more complex indirect method in which the tiles could be laid as they would appear in the final work.