The thermal bath complex of Baiae, located at the bay of Naples, is the most famous and prominent example of a roman Spa. Astonishingly, the archaeological remains have not been comprehensively investigated and published until now. For my PhD dissertation I have examined all archaeological remains and can reconstruct the development of the complex in more detail than previously available. This paper will present the major results of my research and critically assess whether Baiae can be identified as the archetype of a Roman Spa.