The Concilium Plebis (English: Plebeian Council or Plebeian Assembly) was the principal popular assembly of the ancient Roman Republic. It functioned as a legislative assembly, through which the plebeians (commoners) could pass laws, elect magistrates, and try judicial cases. The Plebeian Council was originally organized on the basis of the Curia. Thus, it was originally a "Plebeian Curiate Assembly". The Plebeian Council usually met in the well of the comitium and could only be convoked by the Tribune of the Plebs. The assembly elected the Tribunes of the Plebs and the plebeian aediles, and only the plebeians were allowed to vote.
When the Roman Republic was founded in 509 BC, the Roman people were divided into a total of thirty curiae. The curiae were organized on the basis of the family, and thus the ethnic structure of early Rome. Each curia even had its own festivals, gods, and religious rites. The thirty curiae gathered into a legislative assembly known as the Comitia Curiata or Curiate Assembly. This assembly was created shortly after the legendary founding of the city in 753 BC, and it formally elected new Roman kings. During this time, plebeians had no political rights. Each plebeian family was dependent on a particular patrician family. Thus, each plebeian family belonged to the same curia as did its patrician patron. While the plebeians each belonged to a particular curia, only patricians could actually vote in the Curiate Assembly.
Before the first plebeian secession in 494 BC, the plebeians probably met in their own assembly on the basis of the curiae. However, this assembly probably had no political role until the offices of plebeian tribune and plebeian aedile were created that year, in order to end the secession. As a result of the plebeian movement, the patrician aristocracy formally recognized the political power of the plebeian tribune, and thus legitimized the power of the assembly over which the plebeian tribune presided. This "Plebeian Curiate Assembly" was the original Plebeian Council. After 494 BC, a plebeian tribune always presided over the Plebeian Curiate Assembly. This assembly elected the plebeian tribunes and the plebeian aediles, and passed legislation (plebiscita) that applied only to the plebeians.