Concubinage
During the Empire, there existed a legally recognized quasi-matrimonial' institution known as concubinatus, which was, as it were, an inferior sort of marriage. Like a true marriage, it was a monogamous relation; polygamy was never recognized in Roman law. A man could not have two wives, or two concubines, or a wife and a con- cubine, at the same time. Like a marriage, also, it was terminable at the pleasure of either party.
Persons forbidden by the law of nature to intermarry could not live in concubinage, but persons whose intermarriage was forbidden only by the Jus Civile might do so.
While the position of the concubine (concubina) was legally recognized, it was inferior to that of the wife. She was not called uxor, and did not share the rank and position of the man. The offspring of this union (liberi nat.urales) were not under the patria potestas of their father.
But under the legislation of the Christian Emperors they could be legiti- mated, i. e., brought under the potestas of their father by the subsequent intermarriage of their parents. (Note that legitimation of bastards under modern statutes is effected by the intermarriage of their parents whose relations had previously been illicit. The legitimation of the Roman law extended only to the case of the children of concubinage, a lawful relation).