Mosaic is a medium of art that may embody the most meaningful iconography in a culture's most important settings, as in the cathedral of Monreale (below), or it may be a technique of decorative art, an aspect of interior decoration. In mosaics, small tiles or fragments of pottery (known as tesserae, diminutive tessellae) or of colored glass or clear glass backed with metal foils, are used to create a pattern or picture.
Mosaic was used in Antiquity for domestic interior decoration. Mosaics of the 4th century BCE are found in the Macedonian palace-city of Aegina and they enriched the floors of Hellenistic villas, but mosaic floors are particularly associated with Roman dwellings, from Britain (illustration, right) to Dura-Europas. Splendid mosaic floors distinguished luxurious Roman villas across north Africa. In Rome, Nero and his architects innovated the extension of refined mosaics to cover the surfaces of wall and ceilings in the Domus Aurea, built .
When Christian basilicas began to be purpose-built in the late 4th century, wall and ceiling mosaics were adapted to Christian uses. The greatest development of Christian mosaics unfolded in the Byzantine empire including its outpost the Exarchate of Ravenna and its territories in Sicily, and in its late rival Venice, where mosaic encrusts the exterior and interior of [[San Marco di Venezia|St Mark's]. In Western Europe, the demanding techniques of fresco replaced the even more labor-intensive techniques of mosaic.
at Monreale]]
The craft has continued through the ages, kept alive in the Eastern Orthodox tradition especially, and extending to Russia, where Moscow claimed to succeed Constantinople as the "Third Rome." Many modern examples of mosaic exist. M.C. Escher was influenced by Moorish mosaics to begin his investigations into mathematical properties called tessellation.
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