Return of the Prince

They have cast the Prince from his throne on high
And proclaimed a brave new day
They have named it with Freedom's ancient name
In Caesar's ancient way.

They enjoin our souls to seek new goals
Since released from tyranny
And abjure the Prince and his wicked works
For theirs is mastery.

But hear a dusty bugle rave,
the snarling of the drums,
The whisper from a sunken grave
Where the bones are astir:
"He comes! He comes!"

And see his flag of moonlit clouds advance
Across a waste where the cold winds roam.
The ghosts of old go riding
Through the dark to meet him
So shall the Prince come home.
                            --Poul Anderson

(This is from a novel I read nearly thirty years ago. I don't recall the title or much of the storyline, and I'm not certain my memory of the poem is exact...but I still remember the poem).