According to a theory developed by Theodor Mommsen (1887: 468-475), Augustus made senatorial rank hereditary. Henceforth, it is claimed, there was an important difference between the 'senate' and the 'senatorial order.' Access to the 'senate' was obtained in the same ways as in the Late Republic, through tenure of the lowest-ranking senatorial magistracy, the quaestorship. By contrast, the 'senatorial order' encompassed not merely the six hundred former and current office-holders who were full members of the senate, but also their children, grandchildren and great-grandchildren in the male line. By enabling senators to automatically transmit their status to three generations of their agnatic descendants, so the theory goes, Augustus transformed the senate into a hereditary class. The idea of the 'senatorial order' as a hereditary group was adopted in the classic works of Richard Talbert (1984: 39-47), André Chastagnol (1992: 31-48) and Géza Alföldy (2011: 150-62). It is enshrined in the Cambridge Ancient History, Der Neue Pauly or the Oxford Classical Dictionary (Talbert 1996: 326; Galsterer 2000; Burton 2012: 1347).
This paper challenges the idea of senatorial heredity. It argues that like in the Republic, so also in the Early Empire membership in the senate depended on fulfilling a minimum census and holding a Republican magistracy. It is true that the first emperors subjected those persons who stood under the patria potestas of a senator to a variety of new regulations. But those regulations only applied to young men who were preparing to embark on an office-holding career and young women who were expected to marry a senator. Those descendants of senators who did not participate in politics, or who did not have a husband who was a senator, would lose their rank. Far from making senatorial rank hereditary, Augustus and his successors sought to motivate the offspring of senators to participate in politics and invest their wealth into financing public functions in the imperial capital.
The paper begins with a consideration of the literary and epigraphic evidence on which the traditional view is based. What emerges from this analysis is that the Romans had no conception of the 'senatorial order' as a group distinct from the 'senate.' The term ordo senatorius refers to the same group of persons as the word senatus. This problematises the conventional view that not only senators themselves, but also their wives, children, grandchildren and great-grandchildren in the male line enjoyed senatorial rank.
The paper then reconsiders the meaning of the legal regulations that supposedly created the 'senatorial order.' A close reading of the relevant legislation shows that the laws affected not three generations of his descendants, but only those conceived during his lifetime. According to Roman law, the assets managed by these filii familias were the full legal property of a senatorial pater familias. This is the key to understanding the regulations imposed on members of the 'order.' By prohibiting the filii familias of senators from marrying the descendants of slaves, Augustus prevented persons of servile descendants from access to the wealth of senatorial office-holders. Similarly, by barring city councils from forcing the same filii familias to pay for munificence in their home-towns, emperors protected assets that were the legal property of senators themselves.
Behind these laws stand economic considerations. During their political careers, senatorial magistrates were expected to finance expensive spectacles in Rome. By protecting their assets, the emperor enabled senators to carry out these costly forms of public munificence. But these protections extended only to office-holders themselves. Descendants of senators who withdrew from political life lost these privileges. They again became subject to liturgical duties in their hometowns. This is the reason why there is no evidence for the thousands of non-office-holding members of the 'senatorial order,' which are a necessary consequence of the traditional theory that the privileges of senatorial status were hereditary.