The plebs were, in ancient Rome, the general body of free Roman citizens who were not patricians, as determined by the census. The precise origins of the group and the term are unclear, though it may be that they began as a limited political movement in opposition to the elite (patricians) which became more widely applied.
In Latin the word plebs is a singular collective noun, and its genitive is plebis.
The origin of the separation into orders is unclear, and it is disputed when the Romans were divided under the early kings into patricians and plebeians, or whether the clientes (or dependents) of the patricians formed a third group. Certain gentes ("clans") were patrician, as identified by the nomen (family name), but a gens might have both patrician and plebeian branches that shared a nomen but were distinguished by a cognomen, as was the case with the gens Claudia.
The 19th-century historian Barthold Georg Niebuhr held that plebeians began to appear at Rome during the reign of Ancus Marcius and were possibly foreigners settling in Rome as naturalized citizens. In any case, at the outset of the Roman Republic, the patricians had a near monopoly on political and social institutions. Plebeians were excluded from magistracies and religious colleges, and they were not permitted to know the laws by which they were governed. Plebeians served in the army, but rarely became military leaders.
Dissatisfaction with the status quo occasionally mounted to the point that the plebeians engaged in a sort of general strike, a secessio plebis, during which they would withdraw from Rome, leaving the patricians to themselves. From 494 to 287 BC, five such actions during the so-called "Conflict of the Orders" resulted in the establishment of plebeian offices (the tribunes and plebeian aediles), the publication of the laws (the Law of the Twelve Tables), the establishment of the right of plebeian–patrician intermarriage (by the passage of the Lex Canuleia), the opening of the highest offices of government and some state priesthoods to the plebeians and passage of legislation (the Lex Hortensia) that made resolutions passed by the assembly of plebeians, the concilium plebis, binding on all citizens.