As they entered Númenor, Men were forbidden to set sail towards Aman. They agreed to this, because they regarded mortality as a gift, and did not envy the Valar and Elves who could not die. For two and a half thousand years Númenor grew in might. Númenórean ships sailed the seas and established remote colonies in Middle-earth. During that time, the Elves of Middle-earth were engaged in a bitter fight with Morgoth's former servant Sauron, who had become the second Dark Lord. The Men of Númenor aided the Elves under Gil-galad yet remaining in Middle-earth. But as time went on, Men became evil and rebelled against the Valar and the Elves, over the course of one and a half thousand years, desiring immortality. Tar-Palantir, the penultimate King repented of the evil of his fathers, but it was too late.
The last king, Ar-Pharazôn, hearing that Sauron was striving for the domination of Men and threatening to destroy Númenor, sent a great host to Middle-earth. Sauron's forces became afraid of the might of Númenor, and fled from the service of their master. Perceiving that he could not overthrow Númenor by strength of arms, Sauron humbled himself before the Númenórean King. Ar-Pharazôn was not convinced and had Sauron taken as a prisoner to Númenor. Soon he became the king's advisor, and corrupted the greater part of Númenor to the worship of Morgoth, offering human sacrifices and cutting down Nimloth, the White Tree. During this time, Númenor grew even more powerful thanks to Sauron's counsel, even as its people's joy and span of years lessened.
Sauron convinced Ar-Pharazôn to assail Aman and wrest immortality from the Valar, saying that great kings take what rightfully belongs to them. Sauron's desire was to destroy the Númenóreans and their proud king with the wrath of the Valar (though not to destroy their kingdom), although he underestimated their power. When the Great Armament set foot on Aman, however, the Valar laid down their guardianship and called on Ilúvatar, who broke and remade the world. Eru destroyed Ar-Pharazôn and his Númenórean host, burying them under falling hills until the Dagor Dagorath. To Sauron's dismay, Ilúvatar also had Númenor sunk into the Belegaer, and Aman he removed forever from the circles of the world. The world that had been flat was now spherical, and Aman was only open to Elves, who could still find the Straight Road.
Nine ships carrying men of Númenórean royal blood, descendants of the Lords of Andúnië, of the House of Elros, were carried by the storm of the Downfall to the shores of Middle-earth. They were led by Elendil the Tall, and his two sons: Isildur and Anárion, bringing with them a seedling of the White Tree and the palantíri. These and the Númenóreans already living in Middle-earth carried the title of "The Faithful", signifying their continued devotion to the Valar and Eldar. They allied themselves with Gil-galad and marched in the War of the Last Alliance, in which Isildur cut the One Ring from Sauron's hand.
The followers of Elendil established two Númenórean realms in exile: Arnor, the high kingdom, in the North, and Gondor in the south. Some of the King's Men, enemies of Elendil, established other realms in exile to the south; of these Umbar was the chief. The culture of Númenor became the dominant culture of Middle-earth (thus, Westron, a descendant of the Adûnaic language of Númenor became the lingua franca). The sadness and the shock from the loss of a whole continent lived ever after in the hearts of kings of Númenórean descent. Arda was made spherical, and Aman was put beyond it, out of the reach of mortal men. Sauron, although bereft of the shape in which he had wrought so great an evil that he could never appear fair in the eyes of men again, escaped from Númenor and returned to Middle-earth once more.
It is a curious chance that the stem talat used in Q[uenya] for 'slipping, sliding, falling down', of which atalantie is a normal (in Q) noun-formation, should so much resemble Atlantis.In any case, the resemblance of the names fits in with Tolkien's legendarium as a history lost to myth and legend.