Atlantis (stargate)

In the science fiction television series Stargate Atlantis, the spin-off of Stargate SG-1, Atlantis is a city-sized starship originally located in the Pegasus galaxy. Atlantis serves as the base of operations for the main characters, from which they explore other planets through the Stargate. Based on the ancient Greek accounts of the Lost City of Atlantis, according to the mythology of the show, the city was built by an advanced race known as the Ancients.

Atlantis was built millions of years ago by the Ancients. The city resided in Antarctica on Earth until five to ten million years ago, when a deadly plague prompted the Ancients to relocate it to the Pegasus galaxy. There, it served as the Ancients' capital as they built a new system of Stargates and seeded many worlds with humans. However, the Ancients' activities gave rise to a powerful new species, the Wraith. With their vastly superior numbers, the Wraith drove the Ancients from their holdings until only Atlantis was left, defended by its powerful shield and a network of armed satellites. The Wraith laid siege to Atlantis for one hundred years until the Ancients, unable to see a path to victory, submerged the city and returned to Earth through the Stargate. There they merged with the native human population, and their accounts of Atlantis gave rise to the classical myth of the Lost City. Atlantis itself lay on the ocean floor, empty and dormant, for ten thousand years.

The Lost City of the Ancients is first mentioned by Daniel Jackson in the season 6 finale of Stargate SG-1, "Full Circle". In the episode, he directs SG-1 to a tablet that mentions the Lost City, and tells them that there are powerful weapons there capable of defeating Anubis. The search for the Lost City continues through season 7 of SG-1, and although the team finds the Ancient outpost in Antarctica, the location of Atlantis itself remains a mystery. In the Stargate Atlantis premiere "Rising", Jackson discovers that the Stargate address to Atlantis contains eight symbols, meaning that it is in another galaxy. The multi-national Atlantis Expedition, led by Dr. Elizabeth Weir, is formed to investigate the city, with the knowledge that they might be unable to return as they cannot bring Earth's sole ZPM with them.

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