Opus Siliceum is a masonry technique used in ancient Roman and Italian architecture, in which large stone blocks were assembled without mortar. This technique was particularly preferred for early fortifications, temples, and other monumental structures. The blocks were usually carefully hewn and fitted precisely together, ensuring high durability for the structures.
It was especially used by the Etruscans and Romans and is commonly found in the regions of Latium, Etruria, and Campania. It is associated with the megalithic building tradition and evolved into different versions during the Greek and Roman periods.