Portia's death is reported to the audience twice in Act IV sc.3.
1. Brutus tells Cassius that Portia died by swallowing hot coals. Since Brutus had been away on his military campaign and on hearing that Octavius had joined forces with Antony, she had become very upset and mentally distracted. When she was left unattended she swallowed hot coals of fire and died:
"Impatient of my absence,
And grief that young Octavius with Mark Antony
Have made themselves so strong:--for with her death
That tidings came;--with this she fell distract,
And, her attendants absent, swallow'd fire."
Brutus offers evasive replies, and fortunately for him Ligarius, whom he had sent for, is heard knocking at his door. Brutus hurrriedly asks Portia to leave saying that he will reveal everything to her later, "and by and by thy bosom shall partake/The secrets of my heart...Leave me with haste." And she being the obedient wife does so. 2. A little later Messala repeats the same news that Portia is dead.
Brutus being a true roman, bears this tragic news stoically and remarks:
Moreover, Brutus does not waste time mourning Portia's death, but straightaway gets ready to meet his enemies and wage war against them and rout them completely:
"There is a tide in the affairs of men,
Which, taken at the flood, leads on to fortune;
Omitted, all the voyage of their life
Is bound in shallows and in miseries.
On such a full sea are we now afloat;
And we must take the current when it serves,
Or lose our ventures."