In ancient Rome, the plebs was the general body of free Roman citizens who were not patricians, as determined by the census. From the 4th century BC or earlier, they were known as commoners (part of the lower social status).
Literary references to the plebs, however, usually mean the ordinary citizens of Rome as a whole, as distinguished from the elite—a sense retained by "" in English. In the very earliest days of Rome, plebeians were any tribe or clan without advisers to the King. In time, the word – which is related to the Greek word for crowd, plethos – came to mean the common people.
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.