Legal Definitions - matrimonium non justum

Matrimonium non justum is a Latin term from ancient Roman law that translates to "not a just marriage" or "an unjust marriage." It refers to a union between two people where one or both individuals lacked the specific legal capacity, known as conubium, to enter into a fully recognized Roman marriage.

In Roman law, conubium was a crucial legal right that allowed individuals to form a valid marriage according to Roman customs and laws. Without it, even if a couple lived together as husband and wife, their union was not considered a "just" marriage in the eyes of the law. A key consequence of a matrimonium non justum was that while any children born from such a union were considered legitimate, they were not subject to the father's absolute legal authority (known as patria potestas), which was a fundamental aspect of family law for children born of a "just" marriage.

Here are some examples illustrating this concept:

• Example 1: A Roman Citizen Marrying a Foreigner
  Imagine a Roman citizen, who possessed conubium, wishing to marry a woman from a neighboring foreign kingdom who did not have the right of conubium with Roman citizens. Even if they went through a ceremony and lived together, their union would be classified as a matrimonium non justum under Roman law. The children born to them would be considered legitimate, but the Roman father would not hold patria potestas over them, meaning he wouldn't have the full legal rights and control over their lives and property that a father in a "just" marriage would.

• Example 2: A Free Roman Citizen Marrying a Slave
  Consider a wealthy Roman citizen who falls in love with and attempts to marry one of his household slaves. In ancient Rome, slaves were considered property and generally lacked the legal capacity to enter into a formal marriage with a free person. Therefore, any such union would be a matrimonium non justum. While the couple might live together, their relationship would not be recognized as a legal marriage, and any children born would typically follow the status of the mother (meaning they would be born into slavery) and certainly would not be under the father's patria potestas.

• Example 3: A Roman Citizen Marrying a Peregrinus Without Specific Rights
  During certain periods of Roman history, a Roman citizen might wish to marry a peregrinus – a free person living within the Roman Empire but who was not a Roman citizen and did not possess specific grants of conubium. For instance, a Roman soldier might marry a woman from a conquered province who was a free resident but lacked Roman citizenship and the right to marry a Roman citizen. This union would be a matrimonium non justum because the peregrinus lacked the necessary legal capacity. The children would be legitimate but would not fall under the Roman father's patria potestas, and their legal status might be complex, often following the mother's non-citizen status.