The removal of all danger from without would induce his subjects to luxuriate in idleness, as they would be no longer restrained by the fear of an enemy or by military discipline. To prevent this, he strove to inculcate in their minds the fear of the gods, regarding this as the most powerful influence which could act upon an uncivilised and, in those ages, a barbarous people. But, as this would fail to make a deep impression without some claim to supernatural wisdom, he pretended that he had nocturnal interviews with the nymph Egeria: that it was on her advice that he was instituting the ritual most acceptable to the gods and appointing for each deity his own special priests.
Hor Book I Chapter 19: Numa's Religious Institutions.

First of all he divided the year into twelve months, corresponding to the moon's revolutions. But as the moon does not complete thirty days in each month, and so there are fewer days in the lunar year than in that measured by the course of the sun, he interpolated intercalary months and so arranged them that every twentieth year the days should coincide with the same position of the sun as when they started, the whole twenty years being thus complete.
Hor Book I Chapter 19: Numa's Religious Institutions.

Look, who is he I may discern from far By olive-branch and holy emblems known? His flowing locks and hoary beard, behold!
Vrg Book VI Chapter 31: The future (cont.)
By Anchises

Every alteration of a man's life is dangerous to him; but madness only could induce one who needs nothing and is satisfied with everything to quit a life he is accustomed to
Plt Numa, chapter 5: Election of Numa as king. He needs persuation

So Numa forbade the Romans to represent God in the form of man or beast, nor was there any painted or graven image of a deity admitted amongst them for the space of the first hundred and seventy years, all which time their temples and chapels were kept free and pure from images
Plt Numa, chapter 8: Religious reforms by Numa

He is also much to be commended for the repeal, or rather amendment, of that law which gives power to fathers to sell their children; he exempted such as were married, conditionally that it had been with the liking and consent of their parents
Plt Numa, chapter 17: Other regulations (cont.)

Numa, calculating the difference between the lunar and the solar' year at eleven days, for that the moon completed her anniversary course in three hundred and fifty-four days, and the sun in three hundred and sixty-five, to remedy this incongruity doubled the eleven days, and every other year added an intercalary month, to follow February, consisting of twenty-two days, and called by the Romans the month Mercedinus.
Plt Numa, chapter 18: Calendar reforms by Numa

The sole and only hope of respite or remedy for human evils was in some happy conjunction of events, which should unite in a single person the power of a king and the wisdom of a philosopher,
Plt Numa, chapter 20: No war during the reign of Numa.