A type of opus sectile in which fine geometric patterns of colored stone are inlaid in stone matrices. Cosmati work was used for pavements in church floors, as well as decoration on pulpits, choir screens, tombs, and altars. The technique is named after a family of artisans who ran a workshop in Rome that flourished in the 12th and 13th centuries. Web resource here.
Cosmati work pavement. Basilica of San Clemente, Rome. 12th century.