It seemed to Frodo that he was lifted up, and passing over he saw that the rock-wall was a circle of hills, and that within it was a plain, and in the midst of the plain stood a pinnacle of stone, like a vast tower but not made by hands.
They took me and they set me alone on the pinnacle of Orthanc, in the place where Saruman was accustomed to watch the stars.
So it was that when summer waned, there came a night of moon, and Gwaihir the Windlord, swiftest of the Great Eagles, came unlooked-for to Orthanc; and he found me standing on the pinnacle.
Frodo peering forward saw in the distance two great rocks approaching: like great pinnacles or pillars of stone they seemed.
Westward he looked and saw the broad pastures of Rohan; and Orthanc, the pinnacle of Isengard, like a black spike.
There are no more uses of "pinnacle" in the book.
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She wrote the book at the pinnacle of her fame.
At the pinnacle of her success, she was earning over a million dollars a year.