The development or change of styles is usually considered as a process directed by persons: the artist, the patron, and sometimes intended audience or public. This book offers a different perspective on style formation, taking as a starting point the presence and agency of artefacts. Inspired by recent innovative concepts in archaeology, and psychology, it focuses on the decades around 1800, and reconstructs how the new object scapes that came into being in Rome and Paris, as a result of the massive migration of objects caused by the political upheavals of the period 1789-1815, shaped the formation of Neo-Classicism. The author offers explanations of style formation that go beyond traditional artistic or aesthetic considerations. The laboratory for this investigation is Piranesi's Museo, the artefacts that were created there, and their biographies.