Gaius Terentilius Harsa or Arsa, better known simply as Terentilius, was a plebeian tribune in Rome around 462 BC.
Terentilius agitated for a formal code of laws in the early days of the Roman Republic. He took advantage of the fact that the consuls were away on a campaign against the Volsci to pressure the Roman Senate, controlled by patricians, for the code.
The patricians made a show of making peace with Terentilius, but in fact had no intention of codifying the laws at his request. The later Florentine writer Niccolò Machiavelli commented that this was similar to the Florentine 'Ten of War' that was eventually reinstated once the people realized it was the excessive abuse of authority that was despised, not the title or function of the office itself.
The story of Terentilius comes to us from one source, Book III of Livy's History.