Beware the Ides of March.  What does it mean?  It marks the date in 44 B.C. that Roman dictator Julius Ceasar was murdered by as many as 60 of his own senators, including his own protegy, Marcus Brutus.

Caesar was scheduled to leave Rome to lead a military campaign in what is now Iraq.  His senators already hated him because they were sick of all the decrees he made and then on top of it they were forced to take orders from his underling assistants.  Cassius started the plot and was able to convince his brother-in-law Marcus Brutus to join in.

Caesar should have known so many of his senators hated him, but he dismissed his security force just before he was to leave. He was even handed a warning note as he entered the senate meeting that day but didn’t read it. It told him to Beware the Ides of March.  Ides in Latin means to divide – in this case - beware the halfway point of the month - something Caesar failed to do.  After he entered the hall with Antony, Caesar was surrounded by senators holding daggers. Cassius struck the first blow, hitting Caesar in the neck and drawing blood. The other senators all joined in, stabbing him repeatedly in the head.

Brutus inflicted the final wound, stabbing Caesar in the groin and it was then that Caesar is said to have remarked “Et Tu Brute”, "You, too, Brutus?"

Whether he actually said that is anybody’s guess but Shakespeare dramatized the event in his play “Caesar”.

SOURCE: about.com/history