The Roman system of classes was instituted in the reign of the king Servius, somewhere around the latter half of the sixth century BCE before Rome became a republic. He considered it necessary to organise the entire Roman citizenry according to their financial status into ranks, principally for military and political purposes. It was arguably the first census ever held, at least in the western civilizations.
Accordingly the Roman population was then divided into both classes and centuries. The division into centuries was politically important, as the citizens voted for the senior magistracies (consules and praetores) in the comitia centuriata (= the centuriate assembly).1 A century represented a certain amount of wealth rather than a number of individuals. The result was that the richer classes represented a larger number of centuries while actually being the smaller portion of the population. Livy (Ab urbe condita 1:43) tells us that the first class consisted of people who owned property valued at 100 000 asses (the coinage of the time) or more, which represented 80 centuries. This class was responsible for their own military equipment, and wore full armour, obviously being able to afford and maintain it.
Additionally, there were twelve centuries of knights, being persons who were wealthy enough to also equip and maintain a horse. Needless to say, these twelve centuries fell in the first class as well, and the twelve centuries they represented were additional to the other eighty centuries. The first class also had two centuries of engineers added to it, for purposes of miltary engineering.
The second class owned property between 75 000 and 100 000 asses, and did not have to equip themselves with breastplates (body armour). This class represented 20 centuries. In other words, the first two classes originally represented in total 114 centuries.
The remainder of the classes (six in all), originally represented the remaining 71 centuries, the sixth class forming only a single century despite the fact that the vast majority of people were members of the lower four classes. Obviously the lower the class, the lower the requirement of arms and armour. The fifth class equipped themselves only with slings and stones, while the sixth class was exempt from military service altogether, being too poor to equip themselves.
Practically voting would take place on the basis that the first class was called upon to vote, and then the second. Obviously, depending on which way the vote went, the lesser classes would seldom be called upon to vote, and effectively were disenfranchised, as the first class represented 94 centuries, the second twenty. The rest could hardly hope to influence the outcome of elections in any real way.
The interesting thing about the Roman class system is that it was technically possible (and it did in fact occur at times) that a member of the nobility was incapable of maintaining his position as member of the first class due to lack of money, while it was possible for a pleb to be a member of the first class solely on account of his wealth, but not being eligible for a seat in the senate due to lack of nobility. This all later changed when the man with the money came to be the one that whistled the tune. Cicero2 for instance, became consul despite his rustic background, hailing from the northern parts of Italy, which was only just regarded as being part of Roman Italy – and not always an entirely welcome addition at that.
1 There were other assemblies of the people as well, e.g. the comitia calata which had a more religious function and was called for instance to authorise and witness adoptions and in very early times probably to witness marriages and also the making of wills. The comitia tributa (= assembly of the tribes) had the power to elect the lesser magistrates. All these assemblies lost their importance under the emperors.
2 Who was incidentally Scaevola’s pupil (hem hem).