Augustus' laws; Lex Iulia and Papia Poppaea (18-9 BC) Most important primary sources connected to them
Under Augustus, the Leges Juliae (Julian Laws) of 18 - 17 BC attempted to elevate both the morals and the numbers of the upper classes in Rome and to increase the population by encouraging marriage and having children (lex Julia de maritandis ordinibus) and establishing adultery (stuprum=sexual act with a widow or a virgin as well as adulterium=sexual act with a married woman) as a private and public crime (lex Julia de adulteriis). It had been customary that a father or a husband could persecute daughter and wives for adultery; now with this law any citizen can bring a law suit against a woman believed to have cheated on his husband. To encourage population expansion, the Leges Juliae offered inducements to marriage and imposed disabilities upon the celibate. Augustus instituted the "Law of the three sons" which held those in high regard who produced three male offspring. Free women who produced three legitimate children did not need a guardian anymore. Freedwomen had to produce four children. ForMarrying-age celibates and young widows who wouldn't marry were debarred from receiving inheritances and from attending public games.
Lex Iulia de Adulteriis Coercendis (17 BC)
This law punished adultery with banishment and financial penalties. The two guilty parties were sent to different islands ("dummodo in diversas insulas relegentur"), and part of their property was confiscated. Fathers were permitted to kill daughters and their partners in adultery. Husbands could kill the partners under certain circumstances and were required to divorce adulterous wives.
Augustus himself was obliged to invoke the law against his own daughter, Julia (relegated to the island of Pandateria) and against her eldest daughter (Julia the Younger). Tacitus adds the reproach that Augustus was stricter for his own relatives than the law actually required (Annals III 24)
The extracts below are from later legal codes and textbooks, but are also valuable in the sense that they are based on, and frequently quote from, the actual text of Augustus' laws.
 Ulpian (3rd century)=As written down by Ulpian: The Lex Julia relating to marriage
(Epitome 13-14) By the terms of the Lex Julia, senators and their descendants are forbidden to marry freedwomen, or women who have themselves followed the profession of the stage, or whose father or mother has done so; other freeborn persons are forbidden to marry a common prostitute, or a procuress, or a woman manumitted by a procurer or procuress, or a woman caught in adultery, or one condemned in a public lawsuit, or one who has followed the profession of the stage....
 Justinian (6th century)
Under the rule of Emperor Justinian; The Lex Julia on adultery
(Institutes 4, 18, 2-3) Public prosecutions are as follows....the Lex Julia for the suppression of adultery punishes with death not only those who dishonour the marriage bed of another but also those who indulge in unspeakable lust with males. The same Lex Julia also punishes the offence of seduction, when a person, without the use of force, deflowers a virgin or seduces a respectable widow. The penalty imposed by the statute on such offenders is the confiscation of half their estate if they are of respectable standing, corporal punishment and banishment in the case of people of the lower orders.
(Digest 4, 4, 37) But as regards the provisions of the Lex Julia....a man who confesses that he has committed the offence [i.e. adultery] has no right to ask for a remission of the penalty on the ground that he was under age; nor, as I have said, will any remission be allowed if he commits any of those offences which the statute punishes in the same way as adultery; as, for example, if he marries a woman who is detected in adultery and he declines to divorce her, or where he makes a profit from her adultery, or accepts a bribe to conceal illicit intercourse which he detects, or lends his house for the commission of adultery or illicit intercourse within it; youth, as I said, is no excuse in the face of clear enactments, when a man who, though he appeals to the law, himself transgresses it.