Posthumus is now at the Roman camp in Britain, having joined the Roman forces. He carries with him a bloodstained cloth, sent to him by Pisanio (Act 3, scene 4, line 126) as proof of Imogen's murder. He repents that he had Imogen killed (as he believes), a wife better than himself, for straying just a little. In an example of dramatic irony (where the audience knows what the characters on stage do not), he wishes that Pisanio had obeyed only his just commands, and that the gods had saved Imogen and struck him with more vengeance. Though he has come to Britain to fight against his wife's kingdom, he feels this to be wrong-he has done enough by killing Imogen and will give no wound to her country. He plans to replace his Roman clothes with those of a British peasant, and fight with the Britons against the Romans.
Posthumus's penitence is somewhat unsatisfying and fails to command much sympathy. He regrets ordering Imogen's killing, but still believes she is guilty. Thus, though he has recovered some sense of perspective regarding her alleged sin, he fails to give her the trust she deserves.
As we have seen with Imogen, the shedding and adoption of clothing can carry symbolic weight. Posthumus's decision to shed his Roman soldier's clothes and adopt a British peasant's clothing carries many meanings: his attempt to make amends to Imogen and Britain; his abandonment of attempts to control and punish others and willingness to surrender to his fate; and his penitent attempt to replace impressive clothing with inward worth. He will show more valor than his garments suggest, fight as an unknown soldier without the benefit of his martial reputation, and "begin / To fashion less without, and more within" (lines 32-3).
Note the confusion of roles adopted by Posthumus and Imogen. Imogen, a Briton, has disguised herself as a boy and is serving the commander of the Roman army. Posthumus, another Briton, has been exiled to Rome, is supposed to be serving in the Roman army, and arrived in Britain dressed as a Roman, but has secretly defected to the British cause and is now dressed as a poor Briton. Both characters will, in their disguised roles, find a deeper inner truth than they previously knew.
Cymbeline: Novel Summary: Act 5 Scene 1