Definition of Comitia
A Comitia was the Constitutional Assembly of the citizens of Rome and the legislative body that generated, through its official voice, the potestas (supreme civil powers) and imperium (supreme military powers) delegated to the magistrates. No magistrate could be elected to office, or a law enacted without first convening the Comitia and a majority vote passed on the issue.
In the earliest times, the Comitia met in the Forum and the place where they met was called Comitium. It elected kings, priests, magistrates, passed laws, declared war on enemies or concluded peace treaties with them; it also acted as the last Court of Appeal for Roman citizens. Only Roman citizens, if condemned by a lower Court, had the right of appeal.
Comitia Curiata
The first type of Comitia was called Comitia Curiata and was founded by Romulus. The term curiata means "made up of curiae", as Romulus divided the original founding Gentes (people, family groups) into 30 Curiae, and each Curia was made up of the Patrician Gentes. At this time, therefore, the Plebeians did not partake in the proceedings of the Comitia Curiata, and they enjoyed no political rights.
Voting in the Comitia Curiata took place by a majority of the 30 Curiae. Each Curia had one vote, and within each Curia every citizen would vote individually but the vote of the Curia would be determined by a majority of the votes of the individuals of that Curia.
The Comitia Curiata lasted until the promulgation of the new constitution by and during the reign of Servius Tullius. At this time the whole body of citizens was reclassified into Classes and Centuriae.
The Changes of Servius Tullius
(Sources: Livius I,43 & Dionysius IV.16,VII.59 & Ramsay et Lanciani, page 96)
The model adopted for reorganizing the population of Rome was essentially based on that of a military organization divided into Cavalry (Equites) and Infantry (Pedites).
The Equites were divided into 18 Centuries (Centuriae), and the Pedites into 6 Classes. Each Classis was ranked according to the wealth of their members and contained a number of Centuriae; half of the Centuriae were Iuniuores Centuriae because the age of the men was between 17 and 45 years old; the other half were called Seniores Centuriae and were made up of men over the age of 46. In all, the 6 Classes made up 193 Centuriae.
The ranking of Classes by wealth determined the level of taxes that the State could levy on their citizens. Additionally, when the need arose to assemble an army for defense, each class would contribute according to their means.
Refer to the following table for a listing of the Equites and Pedites into Centuriae and Classes.