Originating in the simple gathering (contio) of the primitive folk, the general assembly of Roman citizens came, under sacerdotal influence, to be grouped in curiae with a view to adding order and solemnity to the meetings. Thus the Romans created the comitia curiata. Not only the curiae, but also the later centuries, classes, and tribes, originally existed independently of the assembly for various administrative purposes and were brought into connection with that institution as convenient systems of organization. At first ceremonial, the comitia curiata came to be used for voting on resolutions. Gradually reducing this earliest organized gathering to a formality, the Romans successively introduced the centuriate and the tribal comitia. Excepting for brief, transitional periods the assembly, whatever its form, admitted all citizens who possessed the right of suffrage. Its power was at first slight vague, and chiefly receptive. Though in the regal period the people occasionally approved or rejected judicial sentences, administrative plans, and even proposals for changes in existing customs submitted to them by the king of his own free will, the only function which at that time they definitely acquired was the election of their chief magistrate.
From the founding of the republic to the decemviral legislation (509-450) the magistrates and senate exercised almost absolute control over the administration. At the very beginning the comitia centuriata—a newly established timocratic institution—assumed the right to enact laws, which for a long time were substantially limited to matters directly affecting the constitution; and the alleged Valerian centuriate statute made of this body a supreme court to which any citizen condemned on a capital charge was granted the privilege of appeal. In practice, however, the law benefited those only of high rank who were accused of political crimes. Meantime a new, more democratic assembly under the presidency of tribunes of the plebs, meeting by tribes after 471, usurped an extensive though ill-defined power of fining and capitally condemning offenders against the sanctity of plebeian officials. But this function, resting upon an act of the plebs only and enforced by threats of violence, was almost nullified by patrician opposition. It was doubtless in this period that voting by heads arose in the comitia centuriata, whence it was adopted by the other assemblies.
The Twelve Tables (451-450) confirmed the comitia centuriata in the rights it had previously assumed; and if not expressly, at least by implication they granted legislative and judicial power to the tribunician assembly of tribes. A Valerian-Horatian statute of 449 provided that resolutions approved by the senate and carried by the latter assembly should have the force of law, just as from the beginning the senatorial sanction (patrum auctoritas) was essential to the validity of curiate and centuriate resolutions and elections. At the same time in conformity with a law of the Twelve Tables an arrangement was made by which the tribunes should bring their finable actions before the tribes and those of a capital nature before the centuries. Soon afterward the patrician magistrates began to use the tribes for the election of inferior officials and occasionally for the ratification of laws.
During the century following the decemviral legislation (450-358) the almost absolute administrative power of the senate and magistrates remained but slightly affected by the comitia. The appointment of a dictator or the establishment of a special judicial commission placed the citizens at the mercy of the government. Although the comitia centuriata acquired the right to ratify or reject declarations of offensive war (427) and though the tribunes succeeded in enacting a few important plebiscites, like the Canuleian and the Licinian-Sextian, the people made little progress toward the free exercise of legislative and judicial functions. With the enactment of a lex de ambitu in 358 the tribes began to legislate concerning magistrates, with reference not only to candidacy and qualifications but soon also to powers and functions and to the creation of new offices. They passed laws on finance and religion and on the qualification and appointment of senators; they assumed the function of ratifying or rejecting proposals for peace (321) and of admitting aliens to citizenship. The tribes and the centuries began regularly to exercise appellate jurisdiction. About the same time the people acquired the function of appointing special judicial commissions, and subjected the dictator to the law of appeal. In an effort to throw off the control exercised by the nobility the Publilian statute of 339 excluded patricians from the tribunician assembly of tribes (a regulation afterward silently abandoned), and in 287 that of Hortensius rendered the approval of the senate and of the patrician portion of it unessential to the validity of the plebiscite. Meanwhile in administrative and in constitutional legislation the comitia tributa made great gains at the expense of the senate and magistrates and of the centuriate assembly.
The period extending from 358 to 287 was accordingly the first great age of comitial legislative and judicial activity. The strong popular tendency then manifested might have created a real democracy, had it not been for (1) the cleverness of the nobles in gaining control of the plebeian tribunate and in using religion as a check on comitial freedom. (2) the rapid expansion of the Roman power, which drew the public mind away from internal politics, and which rendered the assembly not only an inadequate representative of the citizens but also incompetent for the functions devolving upon it. Many years passed, however, before this incompetency became serious. Though henceforth the comitia were in theory sovereign, they remained limited by a want of initiative both in the act of assembling and in the offering of resolutions, by the lack of free deliberation, by the tribunician veto, and by the oblative auspices. After the enactment of the Hortensian statute the comitia tributa enjoyed almost exclusive possession of the legislative function. The larger share fell to the tribunician assembly, which excelled in aggressiveness, and which admitted as much freedom of debate as was consistent with the spirit of the constitution—hence it was preferably termed concilium. Notwithstanding these relative advantages of the tribal assembly the adverse conditions above mentioned led to an era of comitial stagnation (287-232), at the close of which the tribunate of C. Flaminius brought a new outburst of activity (232-201). The assemblies now recovered all they had lost in the preceding age and made fresh gains. Noteworthy are the sumptuary, monetary, private, and family statutes, and the recognition of the right of the people to grant dispensations from existing laws. In the opinion of Polybius the constitution was in this time at its best. The nobles admitted the theory of popular sovereignty, as they could well afford to do in view of their thorough control of all governmental institutions. In the era of the completed plutocracy (201-134) they regularly resorted to the comitia in matters of little political importance or in those in which they felt certain of the results. Under these conditions fewer laws were enacted for the benefit of the masses. The policy of the nobles was to repress individual freedom by subjecting both magistrates and assemblies to the plutocratic machine. Even the comitial judicia were subordinated to this end; and toward the close of the period the people in establishing permanent courts began through legislation to surrender their judicial power to the senatorial class, while the senate, on the other hand, resumed the function of dispensing from the laws and of appointing special courts. In these ways the nobility was making great inroads on popular liberty.
In the beginning of the revolutionary period (134-30) the tribal assembly, liberated for a time from servitude to the plutocracy, became under the presidency of reforming tribunes the ruling power at Rome. Its activity not only embraced the whole field of administration but was directed by the Gracchi to the creation of a new political constitution and to the regeneration of society. But its variable composition precluded consistency of action. Though at times, as when controlled by the rural element of the citizen body, it could be induced to adopt liberal, statesmanlike measures such as the agrarian and colonial laws of the Gracchi, the usual dominance of the ignorant and unprincipled poor of the metropolis inclined it to a short-sighted, selfish course of conduct—rendering it a powerful weapon in the hands either of the demagogue or of the plutocratic senate, equally effective for resisting genuine reforms and for destroying the institutions of the republic. As with the progress of the revolution the conservative checks began to weaken and disappear, the comitia became more and more subject to violence and coercion. The comitial prosecutions of this period partook of the same revolutionary character. From the time of Sulla the assemblies were overshadowed by the military power. Under his dictation they surrendered to the senatorial courts nearly all that remained of their judicial function, and they seriously crippled their legislative power in favor of a reaction to the pre-Hortensian constitution. After a brief interval of bondage to the senate (81-70) they recovered their legislative freedom, only to subserve for the future the alliance now formed between the tribunes of the plebs and the great proconsuls. From the accession of Julius Cæesar to the dictatorship (49) their power rapidly declined. They yielded to him a large share of their legislative and even of their elective function. After a brief period of pretended liberty following the assassination of the dictator, they lapsed with the fall of the republic into utter insignificance.
The comitia had filled a large place in the history of the state. They were the chief factor of constitutional progress and of beneficent legislation. Their development and decline involved the prosperity and the ruin of the republic. For the world they have a higher value. The tribal assembly, supporting the plebeian tribunate, was the storm centre of long, heroic struggles for human rights. The fact that it championed this cause, that it met with some success in the conflict, that a Gracchus deemed it worthy to undertake the social regeneration of the world, has given the institution a universal and a permanent interest.