Having shown how Antony unleashed the power of the mob in Act III, scene 2, Shakespeare in this scene shows us the true nature of the power of the plebeians in Rome, and how, with the vacuum that the conspirators have created through killing Caesar, chaos and anarchy have descended upon Rome. The plebeians meet a poet who bears the same name as one of the conspirators. Even though he protests his innocence and is clearly not a conspirator, the plebeians nevertheless take him away to be beaten to death. Note the picture of chilling violence with which this scene ends:
Tear him, tear him! Come, brands, ho! Firebrands! To Brutus', to Cassius'! Burn all! Some to Decius' house and some to Casa's; some to Ligarius'! Away, go!
Violence and murder rule the streets of Rome, and we see that Antony has taken a gamble in unleashing such irrational violence and cruelty that runs amuk.
In a sense, of course, we find this scene parallelling the assassination of Caesar. Just as Cinna here is the wrong man that the mob are looking for, so, in a sense, Brutus and Cassius were mistaken in their assumption that killing Caesar would end his power and rule. Although they have killed the physical Caesar, they underestimated the power of the symbol that he had become, which Antony is able to use so well to make the mob rise against them. They, too, killed the wrong man in a symbolic sense.