The legends of Atlantis are based not on actual fact, but a combination of truths which when combined gave birth to the legend of Atlantis. The stories about Atlantis, which has never been found, are supported by myths of great cities destroyed suddenly by rising water. Well, that of course happens extensively all over the world every time there is a pole shift, as we have explained. There were lands that sunk under the sea in the Atlantic, but they were no more developed than the bordering lands at the time of the last cataclysms, stories of Atlantis notwithstanding. The Earth was visited by hominoid extraterrestrials in its past, and these hominoids had access to technology that amazed the primitive humans who stood witness. Many cities in and around the European continent went under the waves during the past few pole shifts. This is because the Atlantic, as a widening ocean, tends to drag down the shore lines and outlying islands during each shift. The floor of the Atlantic drops, pulling its perimeter with it. Beyond what has been told about the visitors from the 12th Planet, there is naught to say about rumors about Atlantis. These visitors did not disappear because they went under the waves. They disappeared because they were put into quarantine.
Note: below added during the Dec 14, 2002 Live ZetaTalk IRC Session.
Rumors of Atlantis aside, mankind did not achieve advances beyond what they hold today, in the past. Atlantis was not a human society, but a society composed, dominated, by the advanced homoinoids from the 12th Planet. As we have described, they used crystals for communications, had rocket power, but these equated to no more than mankind had today.