Contubernium was a quasi-marital relationship in ancient Rome between two slaves or between a slave (servus) and a free citizen or other free person. A slave involved in such a relationship was called contubernalis, the basic and general meaning of which was "companion"; the word seems sometimes to have been used as an enduring term of endearment even after a formerly enslaved couple achieved a legal status that allowed them to marry formally. Contubernium was intended to be a lasting, ideally permanent union based on marital affection (affectio maritalis), though the slave's owner retained the power to dissolve the union.
Between two slaves
Roman law regarded the slave as property; slaves lacked legal personhood and therefore could not enter into contracts on their own behalf, including legally sanctioned forms of marriage (matrimonium). Some slaves, however, were permitted or encouraged to form family units—permanent heterosexual unions within which "natural children" (liberi naturales or vernae) might be reared. Roman jurists themselves when discussing case law sometimes refer to unions involving slave contubernales with the terms "husband" and "wife." In inscriptions, most contubernales whose status can be identified are slaves, though liberti and libertae (freedpersons) are also frequent.
On a country estate (villa), a male slave who had proven his reliability might have license to cohabit with a fellow female slave (conserva). The agricultural writer Columella says that contubernium is particularly desirable for the vilicus, the bailiff or overseer of a farm, who was often but not always a slave or former slave. Vernae, slaves who had been born and reared within the household of their enslaved mother, were more likely to be allowed to cohabit as a couple and to rear their own children. Any children born from these unions would increase the master's wealth. Inscriptions reinforce the impression that contubernium was a privilege extended to slaves whose work at higher-skill jobs was valued.
It was possible for contubernium to exist between two slaves with different owners, but the clearest evidence occurs within a household. During most of the Republican and Imperial eras, free Roman women had the right as citizens to own property and retained their property rights within marriage. The mistress of the house would have her own staff, and many of the household's female slaves are likely to have been hers. Documented examples of couples in which each is affiliated with a different gens (extended family or clan) suggest that the two slaves might still belong to the same household or estate, one in the possession of the male head of household and the other of his wife.
In the records kept by well-to-families concerned with lineage, the contubernia of slaves were acknowledged along with family births, deaths, and manumissions. Although a slave lacked legal standing to contract one of the forms of marriage recognized in Roman law, slaves who came from outside Italy would have their own marriage rites and customs. There was no prohibition against slaves considering themselves married by custom in this way, but the protections and liabilities of Roman law on marriage did not apply to them. For example, contubernales could not be prosecuted for adultery.
Between a free woman and a male slave
The jurists of the Digest tend to use the term contubernalis in the context of a marital union between two slaves that is acknowledged by the owner. In practice, the 260 contubernia recorded in inscriptions from the city of Rome (CIL vol. 6), analyzed by Susan Treggiari, show that in this form of quasi-marriage, while most common between two slaves or two former slaves, one partner could be free and the other not. Among the contubernia between a slave and a free person, most often it was the woman who was free, and the male was the slave. There were several scenarios in which this arrangement could be advantageous to the female or male partner or both, but the relationship was typically not between a male slave and his female owner.