Opus quadratum is the term for a building technique used by the engineers of ancient Rome. Rome was famous for its construction projects, many of which are still standing in modern-day Europe. Opus quadratum was the method of building walls, roads, and bridges by placing cut stone blocks in close proximity, sometimes without mortar or another binding substance. The Latin term translates roughly as square work.
The Roman Empire dominated Europe and the Middle East for almost 1,000 years, from 500 BC to the fifth century AD. During this time, it was infamous for its wars of conquest, subjecting whole nations to Roman rule and outright slavery. It did have more positive aspects, including the fact that Rome enjoyed a high level of technology for a society of its time. Its advances in engineering and construction are admired by many to this day. Among the Roman architectural advances were the aqueduct, the dome, and the subterranean sewer.
Opus quadratum was in use from the earliest days of the Roman Empire. The technique involved cutting stone into square or rectangular shapes, as the Egyptians did when building their own temples and pyramids. This method, called ashlar in architectural terms, was very different from the technique of simply piling uncut stones and binding them with mortar, the so-called rubble method used in much of Europe at the time. Once cut, the stones fit snugly together. In early eras, the weight of the stones would often be enough to keep them in place; later, mortar was used to secure them.
The earliest examples of opus quadratum are often uneven, with rough spaces between the stones. This is called Etruscan way stonework, after the early Etruscan civilization of Italy. Eventually, Roman engineers would alternate long stones with short ones to create variety and strengthen the structure. This is known as the Greek way. Later archaeologists could determine the age of a Roman structure by noting these methods and other clues in the construction techniques.
Many structures built with the opus quadratum method are still visible all over Europe. They can easily be detected by use of the Greek way technique, in which the joints in one row of stones are placed over the center of the blocks below them. In addition to its aesthetic qualities, this method lends greater stability to the structure, whether mortar is used or not. A similar technique is used by bricklayers in modern times for the same reasons.