Why does Shakespeare have the soothsayer say beware Ides of March?

Shakespeare included the line "beware the ides of March" spoken by the soothsayer to Julius Caesar in line 1 of Act 1, Scene 2 of his play Julius Caesar because it's a nod to the real story of Julius Caesar. In 44 BC, a soothsayer delivered the same warning to Caesar, who met with tragedy later the very same day.