the tesserae are of various sizes but cut very carefully to form exact shapes, the shapes then fit together like a puzzle. Similiar to marble marquetry. ex. tiger assaulting a calf - coloured marbles - second quarter of 4th century AD Rome, Esquiline - Basilica Iunii Bassi opus signinum - mosaic detail
Opus sectile refers to an art technique popularized in Rome where materials were cut and inlaid into walls and floors to make a picture or pattern. Common materials were marble, mother of pearl, and glass. The materials were cut to thin places, polished, and then cut further according to the design.