March 15 - The Ides Of March

Caesar:
Who is it in the press that calls on me?
I hear a tongue shriller than all the music
Cry "Caesar!" Speak, Caesar is turn'd to hear.

Soothsayer:
Beware the ides of March.

Caesar:
What man is that?

Brutus:
A soothsayer bids you beware the ides of March.

Shakespeare borrowed this scene, along with other details of Caesar's demise, from Plutarch's Life of Julius Caesar. An English translation was readily available, but its precise phrasings weren't quite dramatic enough for Shakespeare's purposes. Where he has the soothsayer declaim, "Beware the Ides of March," the more prosaic original notes merely that the soothsayer warns Caesar "to take heed of the day of the Ides of March."

Julius Caesar Act 1, scene 2, 15–19

E Notes - Julius Caesar - William Shakespeare 

William Shakespeare never published any of his plays and therefore none of the original manuscripts have survived. Eighteen unauthorised versions of his plays were, however, published during his lifetime in quarto editions by unscrupulous publishers (there were no copyright laws protecting Shakespeare and his works during the Elizabethan era). A collection of his works did not appear until 1623 ( a full seven years after Shakespeare's death on April 23, 1616) when two of his fellow actors, John Hemminges and Henry Condell, posthumously recorded his work and published 36 of William’s plays in the First Folio.