Jimmy Page and Robert Plant were big fans of Lord of the Rings, it seems. Many of their songs have lyrics that closely mirror the events of the books. I'll give a series of quotes to back this up, it's interesting stuff. Just to prove they had read the book:
"T'was in the darkest depths of Mordor
I met a girl so fair,
But Gollum, the evil one
Crept up and slipped away with her"
-Ramble on, Led Zepplin
Mordor is the land of darkness in the south of Middle-earth, where Sauron has regained power after his long banishment, as described in The Silmarillion. Frodo, the hero of the tale and protector of the one ring, travels through Mordor on his way to The Crack of Doom. Gollum (aka Smeagol) is a twisted hobbit, a disgusting character who held possession of the ring during much of the time it was supposed to have been lost. It's not clear who the "girl so fair" is that Gollum stole. I can't remember when anything like this would have happened in the book. It's possible Plant is making a personal reference to something else using the characters of the book.
Also, look here:
So I'm packing my bags for the Misty Mountains
Where the spirits go now,
Over the hills where the spirits fly
I really don't know.
-Misty Mountain Hop, Led Zepplin
In The Hobbit, The Misty mountains are the destination of Bilbo, Gandalf, and party, who seek to oust Smaug the dragon from the Hall of the King under the Mountain. The spirits could be any number of things; LOTR is fantastical literature.
Now, the lyrics of "The Battle of Evermore", which is clearly about the book, with interpretations after each stanza:
Queen of Light took her bow
And then she turned to go,
The Prince of Peace embraced the gloom
And walked the night alone.
The Queen of light is Eowyn, who leaves Aragorn and joins the army of Rohan. "Walking the night" would most likely refer to Aragorn's passage through The paths of the Dead.
Oh, dance in the dark of night
Sing to the morn-ing light
The Dark Lord rides in force tonight
And time will tell us all.
The Dark Lord is Sauron. From the poem The One Ring: "...And one for the Dark Lord on his dark throne"
Oh, throw down your plow and hoe,
Rest not to lock your homes
Side by side we wait the might
Of the darkest of them all.
This would appear to be Sauron, in the battle of Pelennor fields as described in The Return of the King. He and his army of Uruk-Hai orcs besiege the fortress of Gondor.
I've skipped a few stanzas after that that don't clearly refer to LOTR, or are just Page and Plant rambling on, so to speak. Then:
The pain of war cannot exceed
The woe of aftermath,
The drums will shake the castle wall,
The Ringwraiths ride in black,
The approach of the armies of Mordor are detailed in the book with many hellish drums. The Ringwraiths are the "Nine mortal men doomed to die" in the poem, who've been corrupted by the Rings of Power, and now wander as incorporeal horsemen in the service of Sauron.
Oh dance in the dark of night,
Sing to the morning light.
The magic runes are writ in gold
To bring the balance back.
Bring it back...
At last the sun is shining,
The clouds of blue roll by,
With flames from the dragon of darkness
The sunlight blinds his eyes.
Magic runes, the Dragon, and the sunlight returning are all familiar from Tolkien. They may be thinking of the moon writings on the map in The Hobbit or the runes on the entrance to Moria in The Fellowship of the Ring.
No less, Robert Plant had a dog named Strider, which was also the traveling name of Aragorn.