In Act I, Scene 3 of "Julius Caesar," why does Casca have his sword drawn?
In "Julius Caesar" on the night before the Ides of March, a frightened Casca, with sword drawn against the danger he fears, encounters on a street in Rome Cicero, who asks Casca "why are you breathless? And why stare you so?" (I,iii,3). Casca tells Cicero that he has seen a common slave pass by, holding up his left hand from which "twenty torches joined"(I,iii,17) burn without harming the slave's hand. Also, Casca says that he had just put up his sword near the Capitol when he met a lion that simply stared at him and then passed on. In addition there were men "all in fire" (I, iii,25) who walked up and down the streets, and owls that were out at noon on the streets.
All these bizarre sights Casca interprets as portents of evil to come, believing that the gods are either engaged in civil war, or they are determined to destroy Rome. When Cassius enters the scene, Casca reports these incidents to him. His sword having been drawn earlier may symbol Casca's bloodlust and the future murder of Caesar since he informs Cassius that the senators plan to make Caesar king. To this report, Cassius replies that he would rather kill himself than see Caesar king; furthermore, he tells Casca of a plot to assasinate Caesar and convinces Casca to join the conspiracy:
I know where I will wear this dagger then;/Cassius from bondage will deliver Cassius....That part of tyranny that I do bear/I can shake off at pleasure. (I,iii,89-99)
Readily, Casca replies,
"So can I;/So every bondman in his own hand bears/The power to cancel his captivity. (I,iii,100-103)
That Casca is a bit devious and is rather influential with others is also evidenced in his conversation with Cassius who calls him "dull" (I,ii,57), while, interestingly, shortly before this statement, Cassius has remarked to Brutus that Casca feigns dullness--
However he puts on this tardy form./This rudeness is a sauce to his good wit,/Which gives men stomach to disgest his words/With better appetite--(I,ii,299-302)
--in order for people to better digest what he says and to feel that they have come up on their own with the ideas that Casca surreptitiously suggests.
Casca's been out running around in the storm, which, as he tells Cicero, is one of the scariest things he's ever encountered:
...never till to-night, never till now,
Did I go through a tempest dropping fire.
Either there is a civil strife in heaven,
Or else the world, too saucy with the gods,
Incenses them to send destruction.
The storm has been dropping fire - fire has been falling out of the sky - and Casca seems to believe that there's some sort of cosmic war going on; that, or the gods are sending destruction down onto the earth.
Casca continues to tell Cicero about the storm he's just come through:
Besides--I ha' not since put up my sword--
Against the Capitol I met a lion,
Who glared upon me, and went surly by,
Without annoying me: and there were drawn
Upon a heap a hundred ghastly women,
Transformed with their fear; who swore they saw
Men all in fire walk up and down the streets.
And yesterday the bird of night did sit
Even at noon-day upon the market-place,
Hooting and shrieking. When these prodigies
Do so conjointly meet, let not men say
'These are their reasons; they are natural;'
For, I believe, they are portentous things
Unto the climate that they point upon.
Casca met a lion in the Capitol, which glared at him - and, to protect himself he drew his sword. Even, he says, as he approached Cicero, he has still not put his sword away: "putting up" one's sword is to put it back in its scabbard. Casca is absolutely astonished by the storm - and he hasn't yet regained himself enough to put his sword away!
Hope it helps!