The story of Marcus Postumius Regilensis (which is probably untrue: Livy says that he was a military tribune whereas other writers mention him as a censor) is important in assessing Livy's understanding of the dynamics of popular politics. Postumius was, according to Livy, a commander in a further war against the Aequians. Postumius for Livy was an example not of great military leadership or poor leadership, but of domestic political folly. Postumius was, according to Livy, soon after his victory over the Aequi, stoned to death by his own troops. It is worth pausing over this event- disregarding whether it actually happened or not- and analysing for a moment why Livy believed that a Roman commander might be killed, in such a bloodthirsty way by his own troops. What according to Livy were the principles of the management of politics that Postumius had disregarded which led to his dreadful death?
When Livy introduces Postumius, he tells us that he was 'in some respects a bad man, though the defects in his character did not become apparent until the campaign had been brought to a successful end'. (IV 49). As is typical with Livy's technique- he introduces a character by giving us in parenthesis the indication of their later fate- it is a way of preparing us to read even his praise in a double edged way in order to spot this flaw. Thus for instance when he commends Postumius's 'great energy' in raising troops (IV 49) the reader is automatically drawn to consider what the inverse quality of great energy might be- these subtle strokes of Livy's brush have already painted for us a character, whose details we are searching for. What Livy establishes quickly though is the reasons for Postumius's instant unpopularity with the troops- he promised them the spoils of the town, Bolae, that they had captured, but refused to give them them (IV 49).
However upsetting your troops was a fairly regular occurrence according to Livy- what turned Postumius from an unpopular to a murdered commander was not necessarily his eagerness in offering his troops plunder and then refusing it to them, as his rashness when he returned to Rome. In the forum he announced that 'Unless my men keep their mouths shut on that matter, they had better look out' (IV 49)- Livy prefaces this comment by telling us that it was 'surely unworthy of any reasonable or intelligent person' (IV 49) and after it tells us that the senate and everyone in the assembly were 'shocked' (IV 49). The reason for their shock is presented to us by Livy through the words of the tribune Sextius, he responded to the 'heartless and brutal comment' (IV 49) by shouting 'Men of Rome... do you hear how he threatens his soldiers as if they were slaves.' and Sextius makes much of the 'gasp of horror' that the speech drew forth and then tells his audience that this is how the patricians think of them. (IV 49)
So we have the character sketch provided to us- the indications of great energy, the rash promise followed by the failure to fulfill, the rash statement in the forum- but Livy adds a last touch. When Postumius arrived back at his army, he was hated (IV 50). But again Livy presents us with an account of why he worsened the situation- a quaestor Sestius attempted to punish the troops and was unable to- Postumius
was sent for and made everything worse by his remorseless inquiries and savage punishments and at last, when the crowd had gathered at the cries of some wretched victims whom he had ordered to be crushed to death under a hurdle, he lost control of himself altogether, left the tribunal and ran like a madman to where the attempt was being made to stop the executions. The lictors and centurions were doing what they could to disperse the mob of enraged soldiery, but to no effect: such was the fury of the troops that Postumius was stoned to death- a commander-in-chief murdered by his own men.
I quoted the whole passage because I think it is important to realise how Livy's entire account has been building to this moment- from the moment that he tells us that Postumius had great energy, to the rash sayings in the forum, he wants us to get an impression. We have a steady build up or revelation of character- and from the first we know that the effect will be that Postumius will be revealed to be 'bad'. Livy's art here is of taking this single incident and unfolding to us the cause- or rather letting us discover the cause.
The art though serves a purpose. What Livy wants us to do is to see Postumius as a dangerous politician. Not because he is unable to command men or because he is cowardly but because he is unwise- and rash. We are shown that Postumius throughout lacks the ability to understand the consequences of what he is saying and evaluate those consequences- that Livy is telling us is fatal in a man in a political community consumed by conflict (any political community worth the name one might rightly think). The artistry reinforces the point- because Livy makes an argument through the unfolding events- seeking to display the connection between the 'great energy' of raising troops, all the way to rash promises, speeches and eventually actions and death. Postumius may not have existed- but he does offer us an example both of Livy's style and of a lesson Livy wants to teach about politics. The legacy of Postumius was one of division and suspicion (IV 50): this is important because it reminds us that these kind of actions (and not merely Postumius's hot blooded wrath but his soldiers' hot blooded response) kept the poison of faction from being dissipated.
Livy therefore uses this historical episode to show us something- that temperament in a politician is a key indicy of success. Postumius could have survived had he been a sober patrician- his death was attributable to his rash thoughtless actions and those rash thoughtless actions had an after effect that poisoned Roman politics.