Angered by a food shortage and led by the First Citizen, a Roman mob armed with clubs and other potentially deadly implements, rally to make demands of the Roman ruling class, arguing that the said ruling class are hoarding surplus grain and profiting at the citizenry’s expense. Again led by the First Citizen, the mob is determined to heap its spite on Caius Marcius, a Roman soldier of high repute, this despite the Second Citizen and Menenius Agrippa who respectively laud Caius Marcius’ honor as unimpeachable and dismiss the First Citizen’s seeming noble revolutionary zeal as ignorance and rashness. Anon, Caius Marcius himself makes an appearance and he likewise discredits the First Citizen and his followers. To prove his point he urges the mob to follow him to the wars against the Volsces from whom corn can be plundered. Naturally, loathe to jeapordize their lives for a cause, the citizens disburse and slink away. However, as Caius Marcius joins his brothers-in-arms, Cominius and Titus Lartius, Junius Brutus and Sicinius Velutus, Tribunes of the people, who were made tribunes on account of the ruling class’ concession to the mob, speak unfavorably of Caius Marcius, prognosticating that Caius Marcius’ pride will be his undoing.
At Corioli, a Volscian stronghold which was previously under Roman yoke, Tullus Arfidius, General of the Volscians, warns the Volscian senators of Cominius, Marcius and Titus Lartius who have deployed their Roman armies to oppose the Volscians. The senators assure Aufidius that actually the odds may be stacked in the Volscians’ favor. Presently, the Volscian senators order Tullus Aufidius to join his men. If or when the order is given, Aufidius and his men are to defend Corioli. Mutually wishing eachother the best Aufidius and the senators part.
Volumnia and Virgilia, Caius Marcius’ mother and wife respectively, are sewing and discussing their opposing outlooks with regards the Roman wars aginst the rebelling Volscians (Volumnia is convinced that her son will prevail resoundingly; Virgilia isn’t as confident; indeed she is fearful for her husband’s welfare) when Valeria, Virgilia’s friend, pays a visit with the express purpose of cheering up her friend. Virgilia is reluctant to join Valeria and Volumnia to an outing, however, and chooses to stay home even after Valeria apprises Virgilia of recent news of her husband’s military exploits.
Marcius makes a wager with Lartius, staking his horse that their general, Cominius, has engaged the enemy. Marcius loses the wager and his horse, but he offers to buy it back. Lartius turns down Marcius’ offer, but he, in turn, offers to lend it to Marcius for however long Marcius would care to borrow it (50 years to be precise). Their friendly wager at an end, they assault the walls of Corioli. Presently, they are beaten back to the trenches, angering Marcius who rallies a counter attack. Alas, Marcius’ men balk at the city gates, leaving Marcius to fend for himself inside the city gates. By and by Marcius, who is all bloodied, emerges whilst fending off his enemies, inspiring Lartius to join Marcius and die as his brother-in-arms if necessary.
As the fighting continues, Marcius denounces those Romans whose priority is plunder whilst yet the fighting has concluded. Anon, when intelligence of Cominius in dire straits vis-à-vis Aufidius becomes known, Marcius decides to go to his general’s aid despite Lartius who argues that Marcius, bloodied as he is, is in no condition to pull off such a daring exploit. Marcius persudades Lartius otherwise, however, and the two part.
Marcius rendezvous with Cominius only to find the latter disengaged from the enemy and in tactical retreat. Having informed Cominius that Lartius has brought Corioli to heel, Marcius entreats Cominius to allow him to engage Aufidius. Knowing Marcius’ headstrong ways, Cominius finds himself unable to coax Marcius otherwise and agrees to let Marcius engage the enemy.
Arguing that if the Romans lost the field to the Volscians, then holding Corioli would become untenable, Lartius sets out to join and, if necessary, to aid Cominius and Caius Marcius. He orders the lieutenant, who is to guard Corioli, to dispatch dvisions of Roman soldiers should Lartius give the signal to do so.
Martius engages Aufidius , and the two agree that the first to retreat is the loser. Anon, Volscian soldiers come to Aufidius’ aid only to be driven back by Marcius. Ashamed by the turn of events, Aufidius turns and flees.
Cominius is determined to honor Caius Marcius, who is loathe to be singled out for special treatment. Indeed, Caius Marcius argues that he has only performed his duty. And as countless others had performed theirs, why should Cominius make a special case for Caius Marcius? Cominius will have of none of Caius Marcius’ self-effacing ways however. In addition to a tenth of all the spoils of war, Cominius offers Marcius his—Cominius’--own horse. And as if that wasn’t honor enough, Cominius dubs Caius Marcius Caius Marcus Coriolanus, in effect acknowledging Corioli as Caius Marcius’ domain. Grudingly, Marcius accepts the honors. By and by, Cominius orders Lartius to return to Rome where he is to apprise every Roman of Marcius’ superhuman exploits, when Caius Marcius, now Coriolanus, makes a special request of Cominius: Coriolanus would like an old man of Corioli of whom he was and is still very fond of granted immunity. Cominius is only too glad to grant the request of course, but there’s a snag. Coriolanus fails to recall the old man’s name so fatigued is he from all the fighting. Presently, Cominius orders Coriolanus to have his wounds attended to.
Relating his defeat yet once again vis-a-vis Caius Marcius, Tullus Aufidius describes to a Volscian soldier of his perpetual and inveterate hatred of Caius Marcius. Anon, Aufidius orders the soldier to go and assess the situation at Corioli and to report to him at the cypress grove where he--Aufidius--will be, laying low.