Popular in ancient Rome and the medieval world, opus sectile is a technique for making decorative pavements using cut and shaped pieces of stone (and occasionally other materials). Unlike in the mosaic technique, where uniformly sized cubes (tesserae) are used, opus sectile employs thin, polished slabs that are shaped to define parts of the pictorial or geometric design. Web resource here.
Opus sectile from the Basilica of Junius Bassus, Rome. Ca. 325-350 CE.