Most monumental Roman constructions that can still be seen today are notable for their solidity, building skill, structural resistance, high degree of specialisation, and complexity. One particularly representative form of construction is that of opus caementicium, a type of concrete that is specifically Roman, in terms of both its choice of ingredients and the methods used to prepare and put it in place. This kind of concrete is extremely flexible and suitable for multiple uses, and it could also set underwater. It was used for a wide range of construction elements, from foundations to elevation walls, to ceilings and, with particularly striking effect, vaulted spaces. This encouraged the development of solutions that were innovative not only in technical terms, but also in terms of architectural experimentation. Variations, improvements and particular solutions did appear over time, but always maintaining a considerable degree of technical uniformity, showing how they were part of a recognised and commonly accepted construction system, which was undoubtedly a revolution in ancient construction technique.