Is it ensure, insure, or assure?
type of mosaic work in which figural patterns are composed of pieces of stone or, sometimes, shell or mother-of-pearl cut in shapes to fit the component parts of the design, thereby differing in approach from the more common type of mosaic in which each shape in the design is composed of many small cubes (tesserae) of stone or glass. Although portable stone mosaic works of similar technique were produced in the Near East as early as about 3000 BC, the term opus sectile properly refers to an art that began in the Hellenistic world, perhaps first in Italy, and continued as a European decorative tradition. Opus sectile first appeared in Rome in Republican times (before the 2nd century BC) as pavement in simple geometrical and floral designs. From the 1st century AD there was also a regular production of small pictures of the opus sectile type.