The two years following Augustus' return to Rome have witnessed social legislation attempting to encourage marriage, regulate penalties for adultery, and reduce extravagance.

Lex Julia (or: Lex Iulia, plural: Leges Juliae/Leges Iuliae) refers to a Roman law introduced by any member of the Julian family.

In the narrow sense (especially when used in the English plural form, Julian laws) they refer to a series of laws relating to marriage and morals, introduced by Augustus in 18-17 BCE.

These represent a specific attempt to force the nobles to marry and to have more children, and are more generally meant to encourage large families and increase the Roman population; adultery is establishing as a private and public crime (lex Julia de adulteriis).

In 17, there are resplendent celebrations of ancient ritual, known as the ludi saeculares (Secular Games), to purify the Roman people of their past sins and provide full religious inauguration of the new age.

Although the principate is not an office which can be automatically handed on, Augustus seems to be indicating his views regarding his ultimate successor when he adopts the two sons of his daughter Julia, boys aged three and one who are henceforward known as Gaius Caesar and Lucius Caesar.

Their father Agrippa, after participating in Augustus' celebration, returns to the East as vicegerent of the emperor.