Thermae thieves and pickpockets were known to frequent the baths. The changing room was known as the "apodyterium" (from Greek "apodyterion" from "apoduein" "to take off"). In many ways, baths were the ancient Roman equivalent of community centres. Because the bathing process took so long, conversation was necessary. Many Romans would use the baths as a place to invite their friends to dinner parties, and many politicians would go to the baths to convince fellow Romans to join their causes. The thermae had many attributes in addition to the baths. There were libraries, rooms for poetry readings, and places to buy
Ancient Roman architecture of these developments are described by Vitruvius, writing in the first century AD in his work De Architectura. 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