In the earliest accounts, passed through fragments of the first Roman historian, Fabius Pictor, he is the third son.
[2] Modern historians doubt the historicity of the specific actions attributed to Arruns and other members of his dynasty, regarding them as highly embellished by later accounts.
[3] During his father's reign, he accompanied his elder brother, Titus, and their cousin, Lucius Junius Brutus, to consult the Oracle at Delphi regarding an omen witnessed by the king.
[4] Following the overthrow of the monarchy, traditionally dated to 509 BC, Titus and Arruns went with their father to Caere, while Brutus was elected one of the first consuls.
[5] After a reported unsuccessful attempt by the Tarquins to regain the throne, the Roman tradition places him with his father in command of the Etruscan cavalry at the Battle of Silva Arsia; after Arruns sighted his cousin Brutus, the two charged each other and were each speared to death.