The obvious English word for factio is faction, however, Andrew Lintott notes that in Roman comedies factio implies power from wealth and social status, rather than leadership of a political or economic special interest group which is the accepted meaning in liberal democracy. Rome existed for long enough, and the historical record short enough, that factio pops up with several meanings, including a corrupt oligarchy, but also the Roman optimates which were the noble and conservative families of the Senate.

Lintott argues that because of the vague description of factio in the Roman political record, the political effect of the Roman aristocracy is better determined through how the aristocracy controlled the consulship and their cohesion in the Senate.

The position of consul was originally the domain of the patricians alone, until the third century BC when plebians became eligible for the position through election. It appears that plebians is misleading as the position required Roman citizenship and in the increasing Roman Empire, this was a small privileged minority.

It also appears that the equistrian order (cavalry) and its high barriers of entry (400,000 sequesteres) meant that the plebians were high in the economic strata. These weren't dung shovellers being elected to the consulship, they were new wealthy families, who were outside of the original Roman nobility.

Lintott notes that despite some social mobility, with plebians families being integrated into the Roman aristocracy, the plebian consul's were still small in number:

new names form only about eight percent of the total in the consular lists in the period between the Pyrrhic War and the Second Punic War.

and:

A well known analysis of the period from 232 to 133 BC shows that the 200 consulships were shared between 58 gentes, 26 of which accounted for 159 consulships, and ten of which accounted for 99., effectively half the total.

That suggests that the Roman aristocracy was very cohesive, as well as competitive in the powerful positions, though within a small group of families.

This would suggest that a class reading of Roman politics may be in order, and since it was a democratic system, which combined voting from tribes and the military, that upward pressure from the majority was being dampened by the cohesive patrician class.

There appears that like the British monarchy, the Roman patricians bent as they needed to. For example the political communication between patricians and plebians prior to the establishment of the Tribunes, and when the position was abolished, was usually a riot. Lintott writes :

Moreover, as Cicero recognised, the plebs at Rome, deprived of its tribunes, resorted to the traditional method of riot in order to give vent to its grievances: the restoration of the tribunate of its full powers became desirable as a safety-valve.

Enfranchisement and political representation became important tools in not only political order, but also social and civil order.

The Tribune was a very powerful position, being made sacred while the Tribune was in office such that violence against them was a crime against divine law (not human law) and they also had the power of veto over consuls and the senate. Augustus, in establishing his power, made the emperor's positions equate to Tribune for life - which was more powerful and popular, with both patricians and plebians, than Caesar's constitutional position as dictator for life.

There was constant competition and the seeking of advantage between the patricians and plebians, and in the late republic, popular will was recognized as a very powerful political weapon, such that the nearest thing to what we would call parties developed. These were the optimates and populares. These were Roman conservatives, the optimates, and Roman popular politicians (normally Tribunes and Consuls), or populares, who pandered to the plebs. Which are political strategies that can be viewed under liberal democracy.

In the early republic the dominance of the patricians was shown in legislation as there were bans on marriage between patricians and plebians, as well as bans on plebians entering elected positions, though this changed.

I suspect this was mainly because of Rome's military success and subsequent conquest. This placed stress on the existing patricians to administer Rome, its provinces and new conquests while still supplying the consuls, senators, magistrates and generals. Essentially the franchise of administrative positions was expanded to include plebians, though rich ones that were Roman citizens, because of the demands of empire for an ever increasing number of skilled administrators.

In parallel to the military campaigns of the early republic, the constitution during that time was largely class based. H.H. Scullard argues that early republican Rome was two states; a plebian state and a patrician state. These states did not become unified until after the Gauls seized Rome; when the patricians and plebians became a unitary Roman state.

The positions of the early republic came directly from the regal period. Other than the Consuls, which was a position to replace the magistracy of the King, the other positions and assemblies already existed while Rome was under a monarchy.

This is one aspect of Rome throughout its period of political independence, the constitution was always contiguous, and never underwent revolution. This is consistent with an unwritten constitution where new conventions and constitutional structures are constantly added. The down-side is, that many of these conventions come in times of emergency; such as the positions of dictatorship, tribune, etc. These can be good, it appears that the unification of the patricians and plebians came from the Gaullish threat (which fits Turchin's argument), but we have examples in the modern world of increasing political equality achieved without a state going into emergency.

Arguably the Roman Constitution was so conservative, as oligarchies are, that the only method for constitutional change was emergency. The civil strife of the late republic where Caesar and Augustus sought to change the fundamental nature of the Roman Constitution could only be done through the imposition of emergency. Since Gracchus, this, rather than statutorial or consular change, became the dominant political form of progression.

I think it is a mistake to look at the Roman Constitution in modern liberal democratic terms. Rome was a martial-state; not a nation-state, and not a modern market-state. It was structured for martial success and security. Its magistrates, assemblies and Senate all had military aspects - such that its democratic nature was militarily based. Consuls and Senators were expected to be generals rather than civil servants. And the plebians that made it into the patrician class, or later into the elected positions, were from the wealthy plebian equestrian class (cavalry).

Since a military structure and militaristic society needs to be able to adapt to constant expansion, warring and infrequent catastrophes such as invasion, it makes sense for emergencies to be the driving force behind organisational, and hence constitutional change.

Another aspect of the Roman Constitution, outside of its deeply oligarchic nature, that would help retard and stop constitutional change, was the veto. This was a central political technology in the Roman Magistracy that could stop any legislation by a single person with imperium. It was intended to halt tyranny, especially from the consuls, which it was feared might seek regal powers, but it became an effective means to halt change. The veto was well established in the early republic as a technology, but I don't know how much it was used. I have not seen or read any discussion on its use during this period.

Part of Scullard's argument for their being two class based states in the early republic was that plebians were not allowed to run for elected positions such as consuls. Plebian law from plebian magistracies and assemblies were also not binding on particians, whereas patrician law was binding on plebians. Not surprisingly, plebians, especially rich ones, agitated for legal equality. Additionally the caste nature of this arrangement was enforced by law that prohibited the inter-marriage of patricians and plebians.

During the early republic many of the constitutional and magistrate positions were duplicated in both the plebian and patriciate states; such as the aediles, and there were four assemblies at this point. There was, however, a written component to the Roman Constitution in the early republic which was the Twelve Tables (I will cover them in detail later). This was the writing down of traditional or customary law into statutory legislation which could be termed constitutional. It appears they were ten commandments like - ie be a good person, where good is defined by the tribe, and don't be an immoral asshole, where immoral is defined by the tribe. Morality always being a moving target in human history.

So we have in the early republic the standard template for Roman Constitutional change and advancement for the martial-state's prosperity. It continued the constitutional positions from the regal period, other the Consuls which were created to replace the King, and Rome went conquesting, such that it became a local power, able to siege Etruscan cities as well as help out its Latium and Hernici allies.

The Roman martial-state was slowly on the path of increasing its size, army, wealth and influence through this period, until it was invaded by Brennus' Gauls and the state collapsed as its military was destroyed. A martial-state is nothing without its military power guiding the state, the society and culture.

This emergency led to the reorganisation of the state and constitutional innovation which was the removal of the partician-plebian caste divide. This became the common constitutional basis for the next stage of the Roman Republic - the middle Republic. Which is probably best defined as the period between the Gaullish invasion of Rome and the Second Punic War.