The book deals with the thermal complex built in Rome by the emperor Caracalla between 212 and 216/217 A. D., parts of which were finished by his successors Elagabal and Alexander Severus, and in particular with its architectural decoration - columns with their bases and capitals, entablatures and other architectural parts in marble. The surviving elements and fragments are listed in a comprehensive catalogue by their function, sort of marble, their type and form, with single types of architectual elements emerging from the resulting groups. In the text these architectural elements are examined in two directions: Firstly about their position within the framework of the Roman architectural decorations, about models and parallels of the ornaments used and - naturally - also about their pecularities; a whole chapter deals with the capitals, treating especially the well-known figured capitals from the frigidarium and their importance for the representative character of the decoration mainly in the transverse axis of the thermal building. Secondly the measures of the single architectural parts are analyzed and grouped into different columnal orders, taking into consideration also older documentations from the Renaissance to the early 19th century. On the base of photogrammetric documentations of the single rooms, of other measurements, again of older drawings and - insofar as they exist - some photographs documenting the position of the finds at the moment of the excavation, the single reconstructed orders are assigned to their supposed locations. In a number of plates these proposed reconstructions are presented in computer-based drawings, the single architectural elements and fragments are documented in an extensive volume of illustrations.