Surface of opus mixtum, a construction technique of Roman architecture in which two or more rows of bricks (opus latericium) are alternated with one or more rows of stone (opus incertum). In this case, the stone row is composed of volcanic tuff blocks. This type of technique began to be used during the time of Tiberius and fell out of use during the Antonine period, although it persisted outside of Rome until the Severan period. Later on, it would be adopted by Byzantine and Muslim architecture. In this instance, it concerns a wall documented in the city of Herculaneum.