A Roman mosaic is a mosaic made during the Roman period, throughout the Roman Republic and later Empire. Mosaics were used in a variety of private and public buildings They were highly influenced by earlier and contemporary Hellenistic Greek mosaics, and often included famous figures from history and mythology, such as Alexander the Great in the Alexander Mosaic.
A large proportion of surviving examples come from Italian sites such as Pompeii and Herculaneum, as well as other areas of the Roman Empire. Source: Wikipedia.