What is the thematic significance of Portia's death?

Brutus stands out as an example of Republican stoicism on the battlefield. He describes the cause of Portia's death as, "Impatience of my absence" (4.2.204). His calmness when speaking about his wife's death frightens even Cassius, who remarks that, "How scaped I killing when I crossed you so?" (4.2.202). He is further taken aback by the ease with which Brutus dismisses the topic when Titinius and Messala arrive. Brutus immediately changes the subject, forcing Cassius to take him aside and ask, "Portia, art thou gone?" (4.2.218). Brutus tells him not to speak of her anymore. Later, when Messala asks Brutus if he has heard anything about Portia, Brutus replies, "Nothing, Messala" (4.2.236). Stoicism and honor mean everything to Brutus, and like Hotspur in Henry IV, Brutus refuses to show weakness to his troops.