"Beware the Ides of March" is a famous warning from Shakespeare's Julius Caesar (Act 1 Scene 2), referring to the 15th of March 44 BCE, the day Caesar was assassinated (both in reality and in the play).
Because of Caesar's assassination on the Ides of March, the phrase has become a general warning of impending doom or misfortune; a symbol of potential betrayal, misfortune, and the importance of heeding warnings or even destiny.
Note in the ancient Roman calendar, the "Ides" corresponded with the full moon, which was the fifteenth day of March, May, July, and October, and the thirteenth day of the other months.
- Source: dear Google (with editing)
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I watched "Julius Caesar" (play recording) again recently, and felt being grabbed into it much more than the first time, partially due to APAD I think, as every sentence in there seemed to be a good candidate for APAD. 
For example, in the same Act, Casca (a Roman senator and one of the conspirators who participates in the assassination of Caesar) said: "it was Greek to me", which means something is difficult or impossible to understand.
I did buy a complete works of Shakespeare in London UK and carried it all the way back, hoping that a book from there would help me understand the Bard better :-). But in reality, watching and hearing the sounds of his plays are the best for me.
Also a short clip of CNN video below talking about the phrase's effects, so very interesting!
As today is March the 13th, so "Beware the Ides of March" everyone! 
