In actuality, MacBeth reigned many years and was considered by his subjects, the Scotts, to be a good king.  Shakespear, of course, takes the English side of things.

It is considered bad luck to mention the name of this play in a theatre.  And Shakespear's image of three witches consorting around a cauldron in a wild and lonely spot has become our image of witches as well.  Below is a link to the four scenes which feature the witches.