It's definitely a man's world in Julius Caesar. Characters who display any signs of weakness in the masculine realm of politics and warfare are considered sissies. Women are considered weak and irrelevant (as when Caesar totally disregards Calphurnia's ominous dream so he won't be thought of as a wimp). Portia, one of the play's two female characters, subscribes to the idea that women are feeble and erratic: her infamous declaration, "Ay me, how weak a thing / The heart of woman is!" echoes throughout the play.
Cassius attempts to undermine Julius Caesar's authority as a leader by attacking his manhood, which suggests that, in Rome at least, power and masculinity go hand in hand.
In Julius Caesar, women, who are excluded from politics and public roles, are associated with weakness and inconstancy.