Opus reticulatum

Opus reticulatum (also known as reticulated work) is a form of brickwork used in ancient Roman architecture. It consists of diamond-shaped bricks of tuff, referred to as cubilia,[1] placed around a core of opus caementicium.[2]

Opus reticulatum used on the exterior wall of Hadrian's Villa, which was used as a retreat for the Roman Emperor Hadrian in the early 2nd century.
Opus reticulatum in Pompeii