Mos maiorum – 'Doing the right thing' in ancient Rome

Unwritten codes of behaviour, maintaining standards, behaving ‘properly’ are as old as the hills, at least as old as the Seven Hills of Rome.

The  mos maiorum, loosely translated as ‘ancestral custom’ was the unwritten code of ancient Rome. It included time-honoured principles, behavioural models and social practices that affected every aspect of life in ancient Rome – private, political, and military. It didn’t need explaining except to barbarians.

Of course, written law was the basis of Roman legal practice and jurisprudence, but mos maiorum was what everybody fell back on in cases of doubt or tie break, or if an orator wanted to call on core traditional Roman practice to clinch his argument. By its very nature, it was the core concept of Roman traditionalism and I suspect much eye-rolling went on by the younger generation when it was quoted at them by the older. However, going against the mos maiorum could be tricky as it was the social glue of Rome and beloved of the older generation who usually held the political and economic power in public and social power in the private sphere of the home.

Family and society

The Roman term familia is better translated as ‘household’ as it included every person attached to the owner’s family from the head of household to the youngest slave. Reflecting the patriarchal society itself, the head of a Roman household, the pater familias, was the senior male. The family hierarchy was traditional and self-perpetuating, supported by and supporting the mos maiorum. The pater familias held absolute authority over his familia including the power of death and the legal right to sell any member of his household including his own children.

The familia was an autonomous unit within society and a model for the social order. However, the pater familias was expected to exercise this power with moderation and to act responsibly on behalf of his family. The risk and pressure of social censure if he failed to live up to expectations was also a form of mos. Sanctions did evolve for mistreatment of slaves as the empire grew and women gained more rights and protections, particularly in the third and fourth centuries AD.

The patron/client relationship

The defining social relationship of ancient Rome was that between patron and client. In basic terms, a patron was a person of wealth and influence for whom the client did favours and supported, especially in elections. In turn, the patron would protect the client and hand out commissions, hopefully lucrative. A client might ask the patron for assistance with seeking redress or for advancement of a family member or himself. Having an influential patron enhanced the client’s status. Both words mean different things today, but there are still echoes such as when a distinguished person becomes the patron of a charity and lends that charity status and ‘pulling power’ with the media.
Although the obligations of this ancient relationship were mutual, they were also hierarchical. A patron might himself be under an obligation to someone of higher status or greater power, and a client might have more than one patron, whose interests might come into conflict. And, of course a client of one man might well be the patron of others further down the food chain. Any patron would have several or many clients who would attend upon him each morning in the hope of attracting his attention. If the familia was the basic unit underlying society, these hierarchical networks created the bonds that made a complex society possible.

Although much activity within patron-client relations related to the law courts, patronage was not itself a legal contract; the pressures to uphold one’s obligations were moral, founded on the quality of fides (trust) and, of course,the mos maiorum. Conquerors or governors sent abroad to administer Roman territories established personal ties as patron to whole communities which then might be perpetuated as a Roman family-type obligation.

Tradition and evolution

Suetonius quotes from an edict of the censors from 92 BC, ‘All new that is done contrary to the usage and the customs of our ancestors, seems not to be right.’ Yet because the mos maiorum was custom, not written law, it did evolve over time. Perhaps the ability to keep a strongly-centralised sense of identity while adapting to changing circumstances contributed to the expansion of Rome from a peninsula town to a world power.

The preservation of the mos maiorum depended on consensus and moderation among the ruling elite, but democratic politics, driven by populares (populist leaders) such as Gracchus who favoured the interests of the plebs (plebians), potentially undermined the conservative principle of the mos.

Gaius Gracchus, tribune of the people, addressing the Concilium Plebis (Plebeian Council) Silvestre David Mirys (1742-1810)

Reform was accomplished by legislation, and written law was introduced to replace what had been implied consensus. When plebeians gained access to nearly all the highest offices, the interests of plebeian families who joined the elite aligned with those of the patricians, creating Rome’s nobiles, an elite social status of nebulous definition during the Republic. The plebs and their support of popular politicians continued as a threat to the mos and elite consensus into the late Republic, as noted in the rhetoric of Cicero.

The mos maiorum could be evoked to validate social developments in the name of tradition. Following the collapse of the Roman Republic after the death of his adoptive father Julius Caesar, the ever astute Octavian disguised his radical program as piety toward the mos maiorum on his way to becoming the powerful individual, Augustus.


During the transition to the Christian Empire, Quintus Aurelius Symmachus argued that Rome’s continued prosperity and stability depended on preserving the mos maiorum.  The early Christian poet, Prudentius, dismissed this blind adherence to tradition as “the superstition of old grandpas” (superstitio veterum avorum) and inferior to the new truth of Christianity. Which brings us nicely to Roma Nova.

In a way, it’s an irony that the group of traditional senatorial families who left Rome in EXSILIUM in order to preserve their equally traditional religion and way of life had to abandon a proportion of the mos maiorum fairly rapidly and adopt a radical solution in order to survive. Roma Novan basic tenets and laws were written in a new Twelve Tables of law which evolved over the centuries, yet cultural and guiding aspects of the mos maiorum remained. Service to the state, the family as basic social and economic unit, interdependency, ‘doing the right thing’ and a strong belief in the Roma Novan identity and values wouldn’t seem out of place to a late Republican Roman.


Updated 2024: Alison Morton is the author of Roma Nova thrillers –  INCEPTIO, CARINA (novella), PERFIDITAS, SUCCESSIO,  AURELIA, NEXUS (novella), INSURRECTIO  and RETALIO,  and ROMA NOVA EXTRA, a collection of short stories.  Audiobooks are available for four of the series. Double Identity, a contemporary conspiracy, starts a new series of thrillers. JULIA PRIMA,  Roma Nova story set in the late 4th century, starts the Foundation stories. The sequel, EXSILIUM, is now out.

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