Tribune
Tribune (from the Latin: tribunus; Greek form tribounos) was a title shared by several elected magistracies and other governmental and/or (para)military offices of the Roman Republic and Empire. It derived originally from the representatives of the tribes (tribi) into which the Roman people were divided for military and voting purposes.
The magistracy of Tribune of the Plebs or Tribune of the people (tribunus plebis) was established in 494 BC, about fifteen years after the foundation of the Roman Republic in 509. The plebeians of Rome seceded from the city as a group until the patricians agreed to the establishment of an office that would have sacrosanctity (sacrosanctitas), the right to be legally protected from any physical harm, and the right of help (ius auxiliandi), the right to rescue any plebeian from the hands of a patrician magistrate. Later, the tribunes acquired a far more formidable power, the right of intercession (ius intercessionis), to veto any act or proposal of any magistrate, including another tribune of the people (veto is Latin for "I forbid"). As the chief representative of the Roman plebeians, the tribune's house was required to be open to all at all times, day or night. The tribunes of the plebs were elected by the Concilium Plebis.
The tribune also had the power to exercise capital punishment against any person who interfered in the performance of his duties (the favourite threat of the tribune was therefore to have someone thrown from the Tarpeian Rock). The tribune's sacrosanctity was enforced by a solemn pledge of the plebeians to kill any person who harmed a tribune during his term of office. The tribune was the only magistrate that was able to convene the Concilium Plebis and acted as its president, which also gave him the exclusive right to propose legislation before it. Also, the tribune could summon the Senate and lay proposals before it. The tribune's power, however, was only in effect while he was within Rome. His ability to veto did not affect provincial governors, and his right to sacrosanctity and to help only extended to a mile outside the walls of Rome. In about 450 BC the number of tribunes was raised to ten.
Tribunes were required to be plebeians, and until 421 BC this was the only office open to them. In the late Republic the patrician politician Clodius arranged for his adoption by a plebeian branch of his family, and successfully ran for the tribunate.
When Lucius Cornelius Sulla was dictator he severely curtailed the tribunes of the plebs by invalidating their power of veto and making it illegal for them to bring laws before the Concilium Plebis without the Senate's consent. Afterwards, the tribune was restored to its former power during the consulship of Crassus and Pompey.
Throughout the Republic and its fall, powerful individuals used the tribunes for their personal glory and gain. Clodius and Milo were both tribunes who used violence in the courts and government in order to achieve the needs and requests of Pompey and Caesar. When the Senate refused to grant Caesar Pompey's veterans lands and a further governship of Gaul, he turned to the tribunes with his demands and got them.
Because it was legally impossible for a patrician to be a tribune of the plebs, the first Roman emperor Augustus was offered instead all of the powers of the tribunate without actually holding the office (tribunicia potestas). This formed one of the two main constitutional bases of Augustus' authority (the other was imperium proconsulare maius). It gave him the absolute right of veto and the authority to convene the Senate. Also, he was sacrosanct, had the authority to veto (ius intercessio), and could exercise capital punishment in the course of the performance of his duties.
Most emperors' reigns were dated by their assumption of tribunicia potestas, though some emperors, such as Tiberius, Titus, Trajan, Marcus Aurelius, etc, had already received it during their predecessor's reign. Also, Marcus Agrippa and Drusus II, though never emperors, received tribunicia potestas.