Portia is the wife of Brutus and in Act II, Scene 1 of Shakespeare's Julius Caesar displays qualities of concern, bravery, and intellect, which make her a fitting wife for "the noblest Roman of them all."
There are several reasons why Portia is concerned about Brutus, which are clearly stated in lines 860-930. She begins by stating that Brutus has left their bed late at night and wandered around looking upset. When she inquired about the reason for this, he was secretive and bad-tempered, which is uncharacteristic behavior for him. She states that whatever is afflicting him is having several obvious effects on his behavior, appearance, and disposition:
It will not let you eat, nor talk, nor sleep,
And could it work so much upon your shape
As it hath much prevail'd on your condition . . .
When he pretends that he is sick, she catches him in his lie and points out that if he were sick, he wouldn't be going out in the cold. Moreover, she noticed the conspirators visiting him.
Portia is concerned for Brutus because he has been moody lately, and does not eat or sleep very well. Cassius stops by for confidential meetings that leave him even more agitated.
She attempts to persuade him to confide in her, she tells him to forget that she is a woman and assures him she is capable of keeping her secrets. Portia sets out to prove this to him by cutting her thigh and resisting the urge to cry out.
Brutus is touched by her concern, but just as he is about to confide in her, Ligarius arrives and stops him.