Atlantis

Atlantis was an ancient, advanced human civilisation, infamous for having sunk beneath the waves. It was shrouded in myth and contradiction. Over the course of their lives, the Doctor visited what seemed to be multiple very different versions of Atlantis, learning about different accounts of how and why Atlantis had sunk. Some accounts suggested that three different Atlantises somehow coexisted in human history, while others suggested the contradictory accounts could be reconciled.

Nature
The consensus, millennia after Atlantis's supposed existence, was that it was a myth. For example, Atlantis was an exhibit in the Museum of Things That Don't Exist. (PROSE: The Taking of Planet 5) A textbook from Coal Hill School Library stated that Atlantis was a fictional island first mentioned by Plato - a Greek philosopher. It was supposedly located "beyond the Pillars of Hercules". As told by Plato, the island went to war with Athens, fell out of favour with the gods, and sank beneath the waves. (PROSE: A History of Humankind) The Second Doctor originally believed "the Kingdom of Atlantis" to be a legend, before he realised that he had found his way there. (TV: The Underwater Menace) However, Mike Yates and Jo Grant both considered the existence of Atlantis believable, although they disagreed as to its location; Yates was under the impression that if it existed, Atlantis was meant to be in the Atlantic Ocean, while Jo knew that more recent historical research suggested that it had been part of the Minoan civilisation. (TV: The Time Monster)

The Sixth Doctor once told his companion Flip that there were several versions of Atlantis. (AUDIO: Antidote to Oblivion) The conflicting locations of Atlantis were later used to confuse the directional computer of the Scavenger. (AUDIO: Scavenger) The Seventh Doctor similarly mentioned that there were three "Atlantises" and that he had visited all of them. (PROSE: Transit) Among the various visits made by the Doctor across the globe in the past, "three possible versions of Atlantis" were noted by Jac as UNIT in the 2010s compiled a list of his appearances in order to deduce where the Twelfth Doctor had gone for his final destination. (TV: The Magician's Apprentice)

Indeed, a number of seemingly different versions of Atlantis were encountered or learned about by the Doctor over the course of their lives:


 * The First Doctor met astronauts hailing from "the World-City of Atlantis" on the planet Vortis in the Isop Galaxy. They were scientifically-advanced warmongers who, now controlling all of Earth, had turned their eyes towards interplanetary conquest. The Doctor took solace in the historical fact of their Earthly empire's destruction, and ensured that the party on Vortis were killed by the native species of Vortis before they could escape into the wider universe. (PROSE: The Lost Ones)
 * The Second Doctor discovered an underwater colony of Atlantean survivors south of the Azores, and believed that he had in fact found "the ancient kingdom of Atlantis", which he had previously believed to be a legend. Zaroff likewise referred to the city he had found as "Atlantis". (TV: The Underwater Menace)
 * Multiple accounts documented Atlantis as a Minoan civilisation built on the island of Thera and whose prosperity was based on the Crystal of Kronos. It was notably visited by the Third Doctor on the very day of its destruction by the godlike Chronovore, Kronos. (TV: The Time Monster, etc.)
 * The Dæmon Azal claimed to the Third Doctor that Atlantis had risen to its state of advancement because the Dæmons had helped its development, and that, when the Atlanteans disappointed them, the Dæmons were the ones to destroy Atlantis as a failed experiment. (TV: The Dæmons)

However, other accounts suggested that some of the conflicting data could be reconciled. For example, according to one account, the nature of the Dæmons' experiment on the Atlanteans was to give them the Crystal of Kronos; in this version of events, the Atlanteans' failure to keep Kronos contained was what condemned them in the eyes of the Dæmons, and they let Kronos bring down their wrath, without acting directly. (PROSE: The Quantum Archangel)

The World-City of Atlantis
One version of Atlantis was a scientifically-advanced colonialist empire which existed in the distant past of Earth and came to rule the entire planet, before turning their attention to other galaxies. The First Doctor met an Atlantean expedition on Vortis, realising he was in the distant past when they stated they were from Atlantis. Discovering how dangerous they were, the Doctor refusedto repair their broken space-ships for them, and instead fled, trying to make his way back to the TARDIS while the Zarbi and Menoptera slaughtered the Atlantean warriors who were giving chase to him. (PROSE: The Lost Ones)

South of the Azores
The Second Doctor discovered the ruins of what he believed to be the legendary "kingdom of Atlantis" south of the Azores. Descendants of Atlean survivors survived in the isolated undersea community well into the 20th century, when they were discovered by Professor Zaroff. He proposed to raise their settlement from the ocean floor, even though his process for doing so would have destroyed the Earth. Zaroff died in the attempt due to the Doctor's intervention. (TV: The Underwater Menace)

On Thera
The Minoan Atlantis was founded on the volcanic island of Thera (TV: The Time Monster) near the site of a dormant hive of Sea Devils who had been hibernating for millions of years. (GAME: Lost in Time)

The Atlanteans worshipped many of the same gods as the ancient Greeks, such as Poseidon. The island's Temple of Poseidon was erected around 2000 BC; Dalios, who witnessed its construction as a young man, was king of Atlantis 537 years later, with the Crystal granting them increased longevity. (TV: The Time Monster) According to one account, this Atlantis was the same as the one experimented on by the Dæmons: their civilisation flourished partly because of the Crystal of Kronos, which had been given to the Atlanteans by the Dæmons along with rudimentary instructions on how to use it. (PROSE: The Quantum Archangel) This version of Atlantis was destroyed when released the chronovore Kronos from the Crystal, with the Third Doctor and Jo Grant bearing witness. (TV: The Time Monster)

In the final moments of Atlantis's existence, the Crystal created a localised time eddy, turning Atlantis into a space-time Waypoint. This meant its final moments were frozen in time, infinitely extended, and that the entire location was soaked in vortex energy and connected to other Waypoints across the universe. The Fourth Doctor and K9 Mark I once landed the TARDIS there, only to be temporarily stuck until he refueled using the vortex energy, with the time eddy causing K9 to malfunction. Elsewhere in the city at the same point in time was River Song, trying to rescue the Crystal of Kronos from the waves for the Lux Library Foundation; she was able to get in and out without trouble using her vortex manipulator. She bumped into a third party of visitors, the Tenth Doctor and Martha Jones, who were on a mere pleasure outing.

Later in her timeline, the malfunctioning Project Indigo took Martha to Atlantis. Realising she was in the present, she made a note of the coordinates before activating Indigo again to get to her actual destination. Some time later, she followed this up by returning to the coordinates and calling for UNIT backup. Due to the temporal anomaly, it came in the form of Liz Shaw instead of one of Martha's own contemporaries. The two women were faced with a Sea Devil from the nearby colony, who had been awakened by the vortex-energy manipulation of the Doctors. They got the Sea Devil to agree to parlay, and called in the Doctor, who arrived in the form of the Thirteenth Doctor. (GAME: Lost in Time)

Unidentified
One account suggested that the Time Agency and the Hokrala Corp were both involved in the sinking of Atlantis. This event was considered a failure for the Time Agency. Jack Harkness was also involved. (PROSE: The Undertaker's Gift)

One of Clara Oswald's splinters was an inhabitant of Atlantis. (COMIC: Blood and Ice)

Cousin Octavia visited Atlantis while working for Faction Paradox. (PROSE: Warring States)

Iris Wildthyme visited Atlantis, and told Oliver Lidenbrock of her experiences there. (PROSE: The Big Crunch)

Other realities
In Roma I, Atlantis was a sea city in the Roman Empire. (PROSE: Warlords of Utopia)

Legacy
The Fourth Doctor compared the "lost" human space station Nerva Beacon to Atlantis; they were both the subject of legend. (TV: The Sontaran Experiment) He later recalled the Atlanteans as one of the civilisations which had created twisting underground passageways which he had to run up and down. (PROSE: A Device of Death)

In 1939, the Seventh Doctor asked Heinrich Himmler if he believed in Atlantis, which according to the Nazis was "the secret home of the Master Race." Himmler affirmed that he did. (PROSE: Timewyrm: Exodus)

The Epoch created a world that was very similar to Atlantis. It was destroyed by Bernice Summerfield and Ruth. (AUDIO: The Kraken's Lament, The Temple of Questions, Private Enemy No. 1, Judgement Day)

Behind the scenes
The various televised Whoniverse visions of Atlantis, or at least the ones presented in The Underwater Menace, The Dæmons, The Time Monster, do not necessarily mesh particularly well together.

Noting this, former Producer Barry Letts' noted in his introduction to the first edition of The Doctor Who Programme Guide that Atlantis had three different and incompatible explanations for its destruction. The line in Transit references this. This point would later be enforced in two Big Finish audio plays, and an off-hand reference made on television in The Magician's Apprentice to "three possible versions of Atlantis".

Atlantide