Few building materials have had as large an impact on public architecture as had Roman concrete, the material of choice during the great building campaigns of the Roman emperors. Roman constructions in concrete were both urban and public, serving as primary expressions of Roman power and affiliation with the State. Hydraulic-setting cement was an attractive ceramic medium for imperial buildings. It could be processed at ambient temperature from readily available raw ingredients, and cast into large designated spaces, to produce integral monolithic structures which could be incrementally extended. We examine the social context for the florescence of public construction which accompanied adoption of concrete as a building medium, describe the ways in which building in concrete evolved, review the relevant materials science of the microchemical and micromechanical setting reactions involved, and speculate on the role played by this important ceramic technology in the Roman architectural revolution. -- AATA