During this year while labourers were digging at some depth on land belonging to L. Petilius, a scrivener who lived at the foot of the Janiculum, two stone chests were discovered about eight feet long and four wide, the lids being fastened down with lead.  Each bore an inscription in Latin and Greek; one stating that Numa Pompilius, son of Pompo and king of the Romans, was buried there, and the other saying that it contained his books.  When the owner at the suggestion of his friends had opened them, the one which bore the inscription of the buried king was found to be empty, with no vestige of a human body or of anything else, so completely had everything disappeared after such a lapse of time.  In the other there were two bundles tied round with cords steeped in wax, each containing seven books, not only intact but to all appearance new. There were seven in Latin on pontifical law, and seven in Greek dealing with the study of philosophy so far as was possible in that age.  Valerius Antias says further that they were Pythagorean books, thus shaping his belief to the opinion of the masses [vulgatae opinioni] that Numa was  a disciple of Pythagoras, and trying to give probability to a fiction.
 The books were first examined by the friends who were present. As the number of those who read them grew, and they became widely known, Q. Petilius, the City praetor, was anxious to read them and took them from Lucius.  They were on very friendly terms; when Q. Petilius was quaestor he had given Lucius Petilius a place on the decury. After perusing the most important passages he perceived that most of them would lead to the dissolution of the national religion [dissolvendarum religionum],.  Lucius promised that he would throw the books into the fire, but before doing so said that he should like to find out, if allowed to do so, whether he could reclaim them either by the right of possession or by the authority of the tribunes of the plebs, without, however, disturbing his friendly relations with the praetor. The scrivener approached the tribunes, and the tribunes left the matter for the senate to deal with.  The praetor stated that he was ready to declare on oath that the books ought not to be preserved.  The senate held the praetor's asseveration to be sufficient, and that the books ought to be burnt as soon as possible in the comitium. Whatever sum the praetor and the majority of the tribunes thought a fair price for the books was to be paid to the owner. The scrivener refused to accept it.  The books were burnt in the comitium in the sight of the people in a fire.--Livy, 40.29.
Machiavelli famously treats Numa (the second King of Rome) as more important to Roman history than even Romulus himself and finds in Numa's introduction of religious practice the most important cause of Rome's greatness. Machiavelli emphasizes Numa's skill in creating the instrumental use of religion as a civic glue of a savage people. Following Plutarch, Machiavelli treats Numa's ability to converse with the gods as a useful device to create authority for Numa's legislation (which included a ban on images of gods [see also Cumberland's treatment]). (By contrast to Romulus, Numa was a foreigner and lacked the power of arms to impose his will.) Machiavelli's version of Numa is very similar to Spinoza's version of Moses (in the TTP).* But to the best of my knowledge Machiavelli does not explicitly comment on the quoted passage above.
Livy clearly does not believe that Numa was a philosophical disciple of Pythagoreas. (Not obvious the dates would match up.) And so this is why, perhaps, he does not allow himself comment on the curious fact that Numa's religious doctrines are written in Latin, while his philosophical writings are in Greek--not to mention the clean split between the two topics. To be sure Numa was a Sabine (and there were legends about their connection to Greece). This is curious because the clear implication of the two sets of books is that Numa derived his political use of religion, perhaps even the content, from Pythogorean philosophy and practices adapted to a Roman context. Given that Livy finds that connection improbable, and does not treat the archeological find as evidence for it, the archeological discovery itself stops making sense.*
One is, thus, left with the sense that Livy either finds the archeological discovery completely baffling or (as seems more likely) he suspects the whole thing is staged, but he refuses to dignify that fact with any elaboration.
But regardless of what Livy thinks the true back story on the archeological find was, he recounts without comment how the ruling elites of Rome (of 181bc) decided to burn the (purported) evidence about the true origins of the religious laws. That is, they do not treat Numa as legend. But peculiarly, they explicitly allow that Numa's writings would unmask and thus destabilize Rome's religious laws. This has the effect of creating and reinforcing a taboo on the origins of Rome's religious practices/laws (and its philosophical pre-history).
I do not find it peculiar that Numa's writings would be taken to undermine the origin myths of Rome at a later date. And I also do not find it peculiar that these myths are (thought) important to the civic functioning of the state. But it is peculiar that (i) one lets on that there exists texts that could undermine and (ii) burns these texts publically as a kind of spectacle. (One ought to keep these things secret!) It is a bit frustrating Livy does not comment on this point, especially because he explicitly notes that before they were burned the books had been read by a considerable number of friends of L. Petilius had read them. One imagines that these friends would generate a number of further legends/stories about the contents of Numa's (purported) books.
As an aside, it's interesting to see such an early account of what we would call eminent domain in action. It seems clear that existing practice was in favor of returning the books to the person who found the books on his land no less. But this was overriden by reason of state (as determined by the senate). And it is pretty clear that by refusing the money, the scrivener is, perhaps, protesting the confiscation of what he took to be his property.
Regular readers know, that, thanks to Žižek, I have long been fascinated by Kant's insistence that one must respect a partial taboo on the origin of one's state:
It is futile to inquire into the historical documentation [Geschichtsurkunde] of the mechanism of government, that is, one cannot reach back to the time at which civil society began (for savages draw up no record of their submission to law; besides, we can already gather from the nature of uncivilized human beings that they were originally subjected to it by force). But it is punishible to undertake this inquiry with a view to possibly changing by force the constitution that now exists. (6:339-40 and the German)
I say 'partial taboo' because a purely distinterested inquiry into a state's past would (counterfactually) seem to be permitted. In one sense Kant here agrees with Rome's Senate at the time of the discovery of Numa's (purported) books. It's better not to inquire into the origins tory.
But Kant's analysis simultanaeously (and perhaps unintentionally) also suggests that Numa, whose reputation was one of a man of peace, who did not use force (and, in fact, had Romulus's bodyguard disbanded**), simply could not have played the role of founder of Rome's civil society that Machiavelli (and others) attribute to Numa. Kant does so by (tacitly) relying on a kind of argument familiar from Scottish stadial thought (going back to More): only through force can savages (and first generation Rome is warlike-savage) become civilized.*** So, from Kant's perspective the actions attributed to Numa can't be possible at all.