Calphurnia and Portia are women married to very strong men, during a time when men were stronger than usual. They must be equally strong, in order to endure the trials and tribulations that come with their husbands' positions. Calphurnia's husband, Caesar, is on a mission to conquer Rome; while Portia's husband, Brutus, is out to stop him.
Calphurnia's role in the play is fairly small, in terms of lines of text, etc. However, her role is significant, because she tries to stop her husband's death. She warns Caesar to stay home from the senate, and if he had listened to her, he would have escaped the plot to murder him. Instead, he was coerced by the murderers not to listen to his wife, for such a thing might weaken his image. Calphurnia's dream is foreshadowing, and Caesar's pride causes him to ignore her dream and her warning (and we all know how well that worked out for him).
Now Portia, that's a tough woman. She is desperate to understand what Brutus goes through, even though he tries to shield her from the truth. She stabs herself in the leg to prove she's strong enough to handle that truth, and later swallows hot coals to end her own life. It doesn't get much tougher than that. Her role is more vocal than Calphurnia's, and she tries to keep her husband out of trouble as well, but neither woman can prevent her husband's demise.