§ Of the Rings of Power and the Third Age The Silmarillion

But their stroke was too late. For the Dark Lord had foreseen it, and he had long prepared all his movements; and the Úlairi, his Nine Servants, had gone before him to make ready for his coming. Therefore his flight was but a feint, and he soon returned, and ere the Wise could prevent him he re-entered his kingdom in Mordor and reared once again the dark towers of Barad-dûr. And in that year the White Council met for the last time, and Curunír withdrew to Isengard, and took counsel with none save himself.