The Silmarillion

Then Ar-Pharazôn the King turned back to the worship of the Dark, and of Melkor the Lord thereof, at first in secret, but ere long openly and in the face of his people; and they for the most part followed him. Yet there dwelt still a remnant of the Faithful, as has been told, at Rómenna and in the country near, and other few there were here and there in the land. The chief among them, to whom they looked for leading and courage in evil days, was Amandil, councillor of the King, and his son Elendil, whose sons were Isildur and Anárion, then young men by the reckoning of Númenor. Amandil and Elendil were great ship-captains; and they were of the line of Elros Tar-Minyatur, though not of the ruling house to whom belonged the crown and the throne in the city of Armenelos. In the days of their youth together Amandil had been dear to Pharazôn, and though he was of the Elf-friends he remained in his council until the coming of Sauron. Now he was dismissed, for Sauron hated him above all others in Númenor. But he was so noble, and had been so mighty a captain of the sea, that he was still held in honour by many of the people, and neither the King nor Sauron dared to lay hands on him as yet.

Therefore Amandil withdrew to Rómenna, and all that he trusted still to be faithful he summoned to come thither in secret; for he feared that evil would now grow apace, and all the Elf-friends were in peril. And so it soon came to pass. For the Meneltarma was utterly deserted in those days; and though not even Sauron dared to defile the high place, yet the King would let no man, upon pain of death, ascend to it, not even those of the Faithful who kept Ilúvatar in their hearts. And Sauron urged the King to cut down the White Tree, Nimloth the Fair, that grew in his courts, for it was a memorial of the Eldar and of the light of Valinor.

At the first the King would not assent to this, since be believed that the fortunes of his house were bound up with the Tree, as was forespoken by Tar-Palantir. Thus in his folly he who now hated the Eldar and the Valar vainly clung to the shadow of the old allegiance of Númenor. But when Amandil heard rumour of the evil purpose of Sauron he was grieved to the heart, knowing that in the end Sauron would surely have his will. Then he spoke to Elendil and the sons of Elendil, recalling the tale of the Trees of Valinor; and Isildur said no word, but went out by night and did a deed for which he was afterwards renowned. For he passed alone in disguise to Armenelos and to the courts of the King, which were now forbidden to the Faithful; and he came to the place of the Tree, which was forbidden to all by the orders of Sauron, and the Tree was watched day and night by guards in his service. At that time Nimloth was dark and bore no bloom, for it was late in the autumn, and its winter was nigh; and Isildur passed through the guards and took from the Tree a fruit that hung upon it, and turned to go. But the guard was aroused, and he was assailed, and fought his way out, receiving many wounds; and he escaped, and because he was disguised it was not discovered who had laid hands on the Tree. But Isildur came at last hardly back to Rómenna and delivered the fruit to the hands of Amandil, ere his strength failed him. Then the fruit was planted in secret, and it was blessed by Amandil; and a shoot arose from it and sprouted in the spring. But when its first leaf opened then Isildur, who had lain long and come near to death, arose and was troubled no more by his wounds.

None too soon was this done; for after the assault the King yielded to Sauron and felled the White Tree, and turned then wholly away from the allegiance of his fathers. But Sauron caused to be built upon the hill in the midst of the city of the Númenóreans, Armenelos the Golden, a mighty temple; and it was in the form of a circle at the base, and there the walls were fifty feet in thickness, and the width of the base was five hundred feet across the centre, and the walls rose from the ground five hundred feet, and they were crowned with a mighty dome. And that dome was roofed all with silver, and rose glittering in the sun, so that the light of it could be seen afar off; but soon the light was darkened, and the silver became black. For there was an altar of fire in the midst of the temple, and in the topmost of the dome there was a louver, whence there issued a great smoke. And the first fire upon the altar Sauron kindled with the hewn wood of Nimloth, and it crackled and was consumed; but men marvelled at the reek that went up from it, so that the land lay under a cloud for seven days, until slowly it passed into the west.