Eye of Sauron

"The Eye of Sauron the Terrible few could endure."

- The Silmarillion

The Eye of Sauron was a symbol adopted by the Dark Lord during the Second Age and the Third Age. It was said that few could endure the eye's terrible gaze. The Eye was used on armor and banners of Mordor as a symbol of Sauron's quasi-omnipotence, and was adopted as something of an insignia by Sauron's forces in general.

In the Lord of the Rings novels, the Eye is simply a metaphor for Sauron's overwhelming spiritual presence and his vast farsight, as it is implied that Sauron has a physical body during the events of the novels. There are a few instances of the Eye manifesting in a somewhat physical sense. Once when Frodo looked into the The Mirror of Galadriel and saw the Eye searching for the One Ring, and again when Frodo and Sam were on the slopes of Mount Doom.

"Far off the shadows of Sauron hung; but torn by some gust of wind out of the world, or else moved by some great disquiet within, the mantling clouds swirled, and for a moment drew aside; and then he saw, rising black, blacker and darker than the vast shades amid which it stood, the cruel pinnacles and iron crown of the topmost tower of Barad-dur. One moment only it stared out, but as from some great window immeasurably high there stabbed northward a flame of red, the flicker of a piercing Eye; and then the shadows were furled again and the terrible vision was removed. The Eye was not turned to them: it was gazing north to where the Captains of the West stood at bay, and thither all its malice was now bent, as the Power moved to strike its deadly blow; but Frodo at that dreadful glimpse fell as one stricken mortally."

The Return of the King, Mount Doom

In Peter Jackson's film series however, the Eye is literally a gigantic eyeball composed of energy that sits atop Barad-dûr. In the novels, Sauron's corporeal form is in fact the Eye, and he lacks a humanoid form.