A tribus, or tribe, was a division of the Roman people, constituting the voting units of a legislative assembly of the Roman Republic. The word is probably derived from tribuere, to divide or distribute; a connection with tres, three, is doubtful.
According to tradition, the first three tribes were established by Romulus; each was divided into ten curiae, or wards, which were the voting units of the comitia curiata. Although the curiae continued throughout Roman history, the three original tribes that they constituted gradually vanished from history.
Perhaps influenced by the original division of the people into tribes, as well as the number of thirty wards, Servius Tullius established thirty new tribes, which later constituted the comitia tributa. This number was reduced to twenty at the beginning of the Roman Republic; but as the Roman population and its territory grew, fifteen additional tribes were enrolled, the last in 241 BC.
All Roman citizens were enrolled in one of these tribes, through which they were entitled to vote on the election of certain magistrates, religious officials, judicial decisions in certain suits affecting the plebs, and pass resolutions on various proposals made by the tribunes of the plebs and the higher magistrates. Although the comitia tributa lost most of its legislative functions under the Empire, enrollment in a tribe remained an important part of Roman citizenship until at least the third century AD.
The first three tribes are said to have been established by Romulus, the founder and first King of Rome, shortly after the foundation of the city. Following the Rape of the Sabine Women, the Sabines under Titus Tatius attacked Rome, and successfully entered the city. After fierce fighting, the Sabine women themselves interceded, stepping between their husbands and their fathers to prevent further bloodshed. Peace was concluded, with Romulus and Tatius ruling jointly, and a large Sabine population relocating to Rome; the nascent city was thus evenly divided between Latins and Sabines. At this time (traditionally 750 BC), Romulus divided the people into three tribes, known as the Ramnes or Ramnenses, named after himself; the Tities or Titienses, named after Titus Tatius; and the Luceres or Lucerenses, whose name and origin were obscure to the ancient historians.