Ancient Roman architecture
Although concrete had been used on a minor scale in Mesopotamia, Roman architects perfected Roman concrete and used it in buildings where it could stand on its own and support a great deal of weight. The first use of concrete by the Romans was in the town of Cosa sometime after 273 BC. Ancient Roman concrete was a mixture of lime mortar, aggregate, pozzolana, water, and stones, and was stronger than previously-used concretes. The ancient builders placed these ingredients in wooden frames where they hardened and bonded to a facing of stones or (more frequently) bricks. The aggregates used were often much larger than in modern concrete, amounting to rubble.
Opus quadratum
This technique was used by the Romans from about the 6th century BC, and over time the precision and accuracy of the block cutting improved. The technique continued to be used throughout the age of the Roman Empire, even after the introduction of mortar, and was often used in addition to other techniques. The type of stone, the size of the blocks, and the way the blocks were put together can all be used to help archaeologists date structures that display the technique.