From the 1st century bc onwards the Romans turned bathing into a highly civilized and essentially communal activity. Establishments called balneae or, later, thermae incorporating suites of rooms at different temperatures became a feature both of private and public building. A typical installation would include a tepidarium (warm room, probably without bath), a caldarium (hot, with plunge bath), a frigidarium (cold, also with bath), and an apodyterium (changing-room). Elaborate examples might also include a laconicum (room with dry heat), a swimming bath, an exercise area (palaestra}, gardens and a library. Such a complex provided a central and important social meeting-point, and it seems that access was enjoyed by a wide cross-section of society. The swift expansion of this type of building, both in individual size and geographically across the Roman empire, was undoubtedly helped by the development of new technologies such as the use of concrete to construct wider and higher vaults, and the installation of underfloor and ducted hot-air heating systems (see hypocaust).