A more thorough explanation:

Definition: Justae nuptiae (pronounced juh-stee nuhp-shee-ee) is a Latin term that means "legal marriage" in Roman law. It refers to a marriage between two people who had the legal capacity to wed.

Justae nuptiae was the only type of marriage that created the familial relationship known as patria potestas. This means that if a couple was married under justae nuptiae, the father had complete control over the children and their property.

For a marriage to be considered justae nuptiae, both parties had to have the capacity to enter into a civil marriage with each other. If the union was defective in any other way, it was not considered a marriage at all. However, if there was no conubium (the legal capacity to marry) between the parties, it might still be considered a marriage, but it would not create patria potestas over the children.

Example: If a Roman citizen married another Roman citizen under justae nuptiae, their children would be considered liberi iusti (legitimate children) and the father would have complete control over them. However, if a Roman citizen married a non-citizen, their children would be considered liberi non iusti (illegitimate children) and the father would not have patria potestas over them.

This example illustrates how justae nuptiae was the only type of marriage that created patria potestas over children. If a couple was not married under justae nuptiae, the father would not have complete control over the children and their property.