The action now shifts to the Volscian city of Corioles, where Tullus Aufidius, about to depart for his attack on Rome, tells the Senators of Corioles that the Romans are already prepared for his offensive. But, the Senators are skeptical of the Romans' readiness; they advise Aufidius to take his army into the field as planned and to return to Corioles only if the Romans arrive and besiege the city.
In Rome, meanwhile, Volumnia and Virgilia, Caius Martius's mother and wife, sit sewing together. Volumnia tells her daughter-in-law how she raised Martius to be a great soldier, and takes more enjoyment from his victories than she would from a husband's embrace. She expresses the hope that he will crush the Volscians and Tullus Aufidius in the coming war and insists upon the beauty of bloody wounds. The two women are visited by Valeria, another Roman noblewoman, and the three discuss Virgilia and Martius's son, who takes after his father in his appetite for physical activity and fighting. Then, Valeria tells them the news from the battlefield--while Cominius has taken part of the Roman army to meet Aufidius's forces in the field, Titus Lartius and Martius are leading the rest of the army in a siege against Corioles.
At Corioles, the Volscian Senators come to the walls to parley with Martius and Lartius. Warning the Romans that Aufidius's army will soon return to rescue their city, they send out what troops have stayed behind in a sortie against the besiegers. The Volscians drive the Romans back to their trenches before Martius, cursing his men for their cowardice, leads them back all the way up to gates of the city. However, in the course of the battle, he is cut off from his troops and trapped within the walls of Corioles; Lartius assumes that he is dead. However, Martius single-handedly holds off the Volscians, forces the gate open again, and allows the Roman army to surge in and seize the city.
The ravaging of Corioles begins, while Martius, wounded and bleeding, takes part of the army to join up with Cominius's forces, who are fighting with Aufidius's men. Cominius, whose army is retreating, has not yet heard the news of Corioles's fall, and so he is surprised at the appearance of the bloody Martius and wonders if the Romans have been defeated. Martius assures him that Corioles is in Roman hands, and then he leads Cominius's forces against Aufidius' men, seeking out Aufidius to engage him in one-on-one combat. The two generals meet briefly during the battle, and Martius drives Aufidius and several other Volscians back while the Roman forces pursue their triumph. He has now led the victory over both the city and the battlefield, but Martius selflessly refuses any share of the spoils, leaving them all to his men, who cheer him. He asks them to stop, but Cominius insists that he deserves a new name, Coriolanus, for his valor in the taking of Corioles, and so he is acclaimed as Caius Martius Coriolanus. Meanwhile, the beaten Aufidius curses his Roman nemesis, who has now defeated him five times, and sends messengers to lobby for peace.
We get a brief glimpse of Aufidius, Coriolanus's great opposite number and enemy, making preparations for the war before the scene returns to Rome and to the Roman women. We find Coriolanus's wife and mother in a domestic scene, sitting and sewing, and then gossiping with one of their friends who pays a visit. But the domestic setting sharply contrasts with the words and character of Volumnia, whose influence on her son becomes apparent quickly. Coriolanus's father is never mentioned, and we assume that he died when his son was an infant, meaning that just as the Roman state lacks a king/father-figure, so too does the hero. Instead, he is raised entirely by his mother, who, denied social and political influence as a woman, seeks to exert power through her son. To the other women, she boasts of having sent her son to battle and expresses a rather distasteful delight in the spilling of blood, even Coriolanus's own blood; she claims that the flowing blood of a battle wound "more becomes a man / Than gilt his trophy. The breasts of Hecuba, when she did suckle Hector, look'd not lovelier / Then Hector's forehead when it spit forth blood / At Grecian sword contemning" (I.iii.39-44). And Virgilia and Valeria join in this peculiar celebration of violence, commenting on how Young Martius, the hero's son, caught a butterfly and tore it to pieces with his teeth, as if such behavior were adorable rather than appalling. Coriolanus's character--his bravery and ferocity in battle and his childishness everywhere else--becomes much more understandable when we consider the environment in which he has been raised.
The scenes that follow occur in brief, almost cinematic cuts from one part of the battlefield to another. More than any of Shakespeare's other warlike heroes--Macbeth, Antony, and Othello, not to mention Henry V--Coriolanus appears to us in action, transforming the small Elizabethan stage into a site for siege and sortie, attack and counterattack. This is the hero's greatest moment, and we never doubt his prowess in battle, as he single-handedly opens the gate of Corioles and then, although apparently drenched in his own blood, renews the fight against Aufidius' men. The duel between the two men, in which Coriolanus defeats not only his adversary but several other Volscians, prepares the ground for his later betrayal at Aufidius' hands: We see the defeated Volscian general beginning to suffer from a consuming jealousy--"Five times, Martius, / I have fought with thee; so often hast thou beat me ...my valor's poisoned / With only suffering stain by him (I.x.7-8; 17-18)." Meanwhile, Coriolanus himself proves magnanimous in victory, deprecating his own achievement and generously commending the soldiers for their valor. Here we have the hero at his best, displaying a generosity of spirit on the battlefield that he is never able to extend to the political arena.