Stoics and Epicureans
Compared to Shakespeare's other tragedies, Julius Caesar is severely restrained in language, and allows little comic material to mingle with its elevated manner. (Sir Philip Sidney would have approved.)
The themes pursued in the play are as elevated as the language. Although he was writing from within a profoundly Christian society, Shakespeare explores with subtlety--and irony--the differing religions of Brutus and Cassius, and the way they affect (or fail to affect) their actions. And the choices the major characters are forced to make between private satisfaction and public responsibility are similar to those of the classical Greek and Roman drama.