Sauron's knowledge of the Istari

[Darth Mithrandir]

'Do I not say truly, Gandalf,' said ARagorn at last, 'that you could go whitheresoever you wished quicker than I? And this I also say: you are our captain and our banner. The Dark Lord has nine. But we have One, mighter than they: the white rider. He passed through the fire and the abyss, and they shall fear him. We will go wherever he leads.'

Yet now under the Lord of Barad-dur the most fell of all his captains is already master of your outer walls,' said Gandalf. 'King of Angmar long ago, Sorcerer, Ringwriath, Lord of the Nazgul, a spear of terror in the hand of Sauron, shadow of despair.'

Then, Mithrandir you have a foe to mathc you,' said Denethor. 'For myself, I have long known who is the chief captain of the hosts of the Dark Tower. Is this all you have to say? Or can it be that you have withdrawn because you are overmatched?

Like thunder they broke upon the enemy on either flank of the retreat; but one rider outran them all, swift as the wind in the grass: Shadofax bore him, shining, unveiled once more, a light starting from his upraised hand.
The Nazgul screeched and swept away, for their Captain was not yet come to challenge the white fire of his foe....

I'll just reference the last page from the chapter 'The Seige of Gondor' where Gandalf and the Witch King conversed within the Gate of Gondor. If Gandalf were not at least as powerful as WK, then there would have been no point in his open defiance. Pick up the beginning of chapter 6 'The Battle of the Pelennor Fields' and see that there was more amiss than the white rider that seemed more urgent. The ring had not been found, or he would have known the summon.

Fear of failure most certainly called his attention to the battle field. Fear of Mithrandir, I'm not exactly sure that WK knew who he was. WK did know that no mere man could defeat him (conversation with Dernhelm/Eowyn), and it was common knowledge among the company that any blade that struck him would be destroyed (See the conversation in Rivendell, or just prior after Frodo was stricken by him.

Interestingly enough (and part of my theory in Speculations and another 'what if' scenario ), Merry's sword which was enchanted with a spell from Fornost? was the actual dealing blow. (I seriously doubt this will be covered in the movie ROTK.) [img]smilies/evil.gif[/img] [img]smilies/confused.gif[/img]