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.
Technological history of the Roman military
However, the Romans made many significant technological advances, such as the invention of hydraulic cement and concrete. They used such new materials to great advantage in their structures, many of which survive to this day, like their masonry aqueducts, such as the Pont du Gard, and buildings, such as the Pantheon and Baths of Diocletian in Rome. Their methods were recorded by such luminaries as Vitruvius and Frontinus for example, who wrote handbooks to advise fellow engineers and architects. Romans knew enough history to be aware that widespread technological change had occurred in the past and brought benefits, as shown for example by Pliny the Elder's Naturalis Historia. That tradition continued as the empire grew in size and absorbed new ideas. Romans thought of themselves as practical, so small-scale innovation was common (such as the development of the ballista into the polybolos or repeating ballista). The traditional view is that their reliance on a plentiful slave labour force and a lack of a patent or copyright system have both been cited as reasons that there was little social or financial pressure to automate or reduce manual tasks. However, this view is being challenged by new research that shows they did indeed innovate, and on a wide scale. Thus the watermill had been known to the Greeks, but it was the Romans who developed their efficient utilisation. The set of mills at Barbegal in southern France were worked by a single aqueduct, which drove no fewer than 16 overshot mills built into the side of a hill. They probably were built by the army and supplied flour to a wide region. Floating mills were also used to exploit fast flowing rivers.