Roman Stone Masonry: Volcanic Foundations of the Ancient City
facing of small stone chunks, usually tuff; opus reticulatumrefers to a facing of small tuff pyramids with their square face laid diagonally; opus testaceum refers to brick or tile facing; opus mixtum refers to a facing with alternating panels of tuff opus reticulatum and brick (Sear 1989, 74; Claridge 1998, 44).