23.2.1 (Modestinus,  Rules, book 1). Marriage is the union of male and female and the sharing of life together, involving both divine and human law.
23.2.24 (Modestinus, Rules, book 1). Cohabitation with a free woman is to be considered marriage not concubinage, unless she is a prostitute.
23.1.11 (Julianus,  Digest, book 16). Engagement like marriage comes about by the consent of the parties, and so a daughter-in-power's consent is needed for an engagement as it is for a marriage.
23.2.22 (Celsus, Digest, book 15). If under pressure from his father a man takes a wife, whom he would not have married if he had followed his own inclination, still, though there is no marriage without consent, he contracted a marriage; he is regarded as having preferred to do so.
23.1.12 (Ulpian, On Betrothal, sole book) (pr.) A daughter who does not oppose her father's will [as regards her engagement] is taken to agree. (1) She is free to disagree  only if her father chooses her a fiancé who is unworthy or of bad character.
18.104.22.168 (Paul, Edict, book 35) For an engagement the same people have to agree as for a marriage. Nevertheless, Julian writes that the father of a daughter-in-power is understood to consent unless he explicitly disagrees.
23.2.2 (Paul, Edict, book 35) A marriage can only exist if all agree, that is the parties and those in whose power they are.
27. 'Marriage in the later Republic and Empire was always consensual, that is, by agreement. It existed if the man and woman intended their relationship to be a marriage (and had the necessary parental consent, etc.), symbolized usually by the husband carrying her over the threshold of his house or flat. It ended when one or both of them ceased to have this (firm) intention. Notification (repudium) meant telling the other party that the notifier no longer had the intention to be married, whereupon divorce took effect without more formality. Divorce (divertere) means going one's own way, and since if one spouse goes his or her own way, they are no longer going the same way, either spouse could divorce the other (and originally either spouse's father could do so if the child remained in his power). There was no requirement of mutual consent to divorce, and it made no legal difference.' (Honoré, 1991).
28. Herennius Modestinus was the last classical jurist of consequence. Ulpian alludes specifically to him as a student in responding to a letter Modestinus wrote to him from Dalmatia (Digest 22.214.171.124). He was praefectus vigilum at Rome sometime between A.D. 224 and 244. Among other works, he wrote ten books of Rules.
29. Generally regarded as one of the most brilliant of the classical jurists, Publius Salvius Julianus, consul in A.D. 148, enjoyed a distinguished career that spanned the reigns of Hadrian, Antoninus Pius, and Marcus Aurelius. Hadrian entrusted to him the task of producing the final edition of the Praetor's Edict. He wrote a number of works and is much cited in the Digest.
30. Prominent as a legal thinker in his day, Publius Iuventius Celsus was praetor in A.D. 106 or 107 and consul for the second time in 128. He also served as governor of Asia and on Hadrian's council. His major work was the Digests in thirty-nine books.
31. Some scholars believe that Justinian changed the text from "she is taken" to disagree.