Soon after, an attack from the Volscians, the Roman's archenemies, is announced.  Coriolanus is chosen as a key commander in defending the city.  Two tribunes, representatives of the people, comment on Coriolanus' arrogance and contempt for the people of Rome.

     Coriolanus' mother, Volumnia, is very proud that her son has been chosen as a key commander.  His wife, Virgilia is distraught over the chance that her husband might get killed in battle.  Volumnia can't understand her worries, as she believes military honor is everything, and says she'd rather have eleven sons die bravely at war than have one son survive, devoting his life to idle pleasures.

     Coriolanus then arrives at the city of Corioli, and caught up in the heat of battle, he follows the Volscians inside the city gates.  His soldiers think he must be dead.  After a while, however, Coriolanus emerges, covered with blood.  He inspires his troops with courage and then leaves to aid Cominius, another Roman commander.  When he arrives on the battlefield, he is thrilled because he is able to battle Aufidius, the greatest warrior of the Volscians.  He defeats Aufidius, but Aufidius escapes before Coriolanus can kill him.  This victory earns Caius Martius the new name "Coriolanus."  Aufidius vows vengeance on Coriolanus.

     When Coriolanus returns to Rome, the senate chooses him to run for consul, but he does not readily accept.  He believes he is a fierce warrior, not a consul.  Plus, he hates to show humility, which would be necessary in order for him to win the respect of the people and be chosen for consul.  The aforementioned Tribunes remark again on Coriolanus' pride and arrogance, and mention how difficult it would be for him to beg consent from the masses to be their consul.

     Under much pressure, Coriolanus finally decides to ask for consulship, yet it soon becomes evident that he is incapable of begging the masses to choose him.  Coriolanus' elitist mindset believes the masses are ignorant lacking principle and character.  He judges them and announces their faults.

     As the Tribunes watch Coriolanus' angry parade, they are pleased, for they wish to convince the masses that Coriolanus is their enemy and should be executed due to his hatred for the Roman people.  Later in the play, they successfully convince the people of this.  A riot breaks out -- not only against Coriolanus but the entire Patrician class.  Volumnia, Coriolanus' mother, begs him to take back his attacks on the people, but he refuses to be humble to the masses.  Coriolanus is banished.

     His career as a fierce warrior is not over, however.  He disguises himself and finds Aufidius.  He explains his story to Aufidius and asks if he can help him conquer Rome.  Aufidius accepts.  Rage erupts in Rome when it is discovered that their key commander has joined their enemy.  Afterwards, we see that Aufidius is growing jealous of Coriolanus' power and popularity with the Volscians. 

     The Volscians prepare for an attack on Rome, but Volumnia, Virgilia, and Coriolanus' young son beg him to spare the city.  Coriolanus cannot refuse his mother.  He feels he owes her his very existence, so he grants her request and spares the city.  Coriolanus mentions that he hates that his young son witnesses this flaw in his character -- his undying allegiance to his mother.