The territory of the rural Latin town of Tibur (Tivoli) constituted one of the most important sites of Roman villa culture in the Republican period. In the summertime, Roman senators were attracted by the cool atmosphere of the Tiburtine slopes in order to escape the bad climatic and narrow spatial conditions in Rome. In his study, Martin Tombrägel discusses the architectural genesis of the earliest Roman otium-villas at Tivoli. A series of imposing elite residences were built here from the early 2nd century B.C. Construction employed the new medium of concrete, and this allowed for the development of adventurous architectural forms. This study offers a comprehensive analysis of the architectural history of the luxury villa. It also probes the origins of this fascinating building type in its social-historical context.