Ancient Roman architecture adopted the external language of classical Greek architecture for the purposes of the ancient Romans, but grew so different from Greek buildings as to become a new architectural style. The two styles are often considered one body of classical architecture. Roman architecture flourished in the Roman Republic and even more so under the Empire, when the great majority of surviving buildings were constructed. It used new materials, particularly concrete, and newer technologies such as the arch and the dome to make buildings that were typically strong and well-engineered. Large numbers remain in some form across the empire, sometimes complete and still in use.