The opus reticulatum technique

Opus reticulatum (reticulated work) is a Roman building technique used to create the face of a concrete wall. Initially, the stones that formed the wall cladding were prepared before installation in an irregular pyramid shape with a square base, then arranged with the base visible while the tip was sank into the concrete.
Subsequently cubilia (cube-shaped bricks) with a perfectly regular square and absolutely uniform base were used, arranged in regular rows with the sides at 45 degrees to the horizontal line. The final effect on the wall was to create a regular diagonal grid.