Macbeth

The Tragedy of Macbeth is a play by William Shakespeare, thought to have been first performed in 1606. Filled with witches and prophecies, it is a fanciful imagining of the rise and eventual fall of Macbeth, a historical king of Scotland about whom virtually nothing is known. A likely motivation in writing the play was to curry favour with King James, as some of its characters are idealised imaginings of James' ancestors. There is a popular notion that the play is cursed, and acting companies preparing to perform it will not speak its title aloud before opening day, referring to it instead as "The Scottish Play".

Macbeth in Ruled Britannia
The Scottish Play, written by William Shakespeare, had been performed often at the Theatre by 1598. Lope de Vega had seen it a few times and admired it. When Vega went to inspect the doings of Lord Westmorland's Men on Ash Wednesday in 1598, he came upon Richard Burbage rehearsing a key speech of the King of Scotland.

Literary comment
While the "Scottish play" is otherwise unidentified, the speech recited by Burbage is from Act 5 Scene 3 of Macbeth, against all probability.