The Paternal Power (Patria Potestas)
The patria potestas, or paternal power, was the sum of the rights and powers enjoyed by the head of a Roman family over the members of his household. In the extent to which it went the patria potestas was one of the most remarkable features of the Roman law. It was the basis of the Roman family, and was an institution of the Jus Civile.
The potestas could be enjoyed only by a Roman citizen, and a loss of citizenship involved also the loss of the potesms. Moreover, it was enjoyed only by the male head of the family, the father, grandfather, etc., and never by the mother, grandmother, etc.
A mother could never exercise the power for she was herself either under the manus of her husband, or under the power of her father in case of a free marriage, or, if a widow, under the tutelage of her own children or other agnates.
A married woman was, indeed, known as a materfamilias, where the marriage was with manus, in which case, since she was under the marital power of her husband, the term materfamilias was the equivalent of filiafamilias rather than paterfamilias. In later times the term materfamilias was applied to any woman of good character whether married or not.