Theodor Mommsen's influential multi-volume work, first published between 1871 and 1888, is a systematic treatment of the intricate workings of the Roman state. The renowned German scholar proposed an original and sometimes controversial understanding of Roman institutions, based around the categories of nineteenth-century constitutional law. The Romans themselves never actually codified their complicated body of law, but by applying a historical approach to describe the development of Roman law Mommsen succeeds in making it more accessible to the reader. He systematises the many diverse legal elements upon which the Roman constitution was based and offers a coherent reading of it. In Volume 3, Part 1 Mommsen gives a detailed account of the various economic and social categories of Roman citizens and subjects, including senators, patricians, plebs, freed slaves, and non-Roman inhabitants of the empire.