The Institutes of Justinian

"Roman citizens are joined together in lawful wedlock when they are united according to law, the man having reached years of puberty, and the woman being of a marriageable age, whether they be independent or dependent: provided that, in the latter case, they must have the consent of the parents in whose power they respectively are, the necessity of which, and even of its being given before the marriage takes place, is recognised no less by natural reason than by law. Hence the question has arisen, can the daughter or son of a lunatic lawfully contract marriage? and as the doubt still remained with regard to the son, we decided that, like the daughter, the son of a lunatic might marry even without the intervention of his father, according to the mode prescribed by our constitution."