Tribune of the plebs
These tribunes had the power to use the People's Assembly (the Concilium Plebis) to support the common people. They could summon the Senate, propose legislation and intervene on the behalf of plebeians in legal matters. Most important of all was the power to veto the actions of the Consuls and other magistrates, to protect the interests of the plebeians. An assault on any plebian tribune was against the law.