As Macbeth is one of the more popular plays in the English language, fleeting references to it crop up in numerous Harry Turtledove works. They rarely have any particular relevance to the plot.
Macbeth in Ruled BritanniaEdit
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.
While the "Scottish play" is otherwise unidentified, the speech recited by Burbage is from Act 5 Scene 3 of Macbeth, against all probability.