Stargate Atlantis (2004)

Stargate Atlantis is set in the city of Atlantis, on a planet called "Lantea" in the Pegasus galaxy. The city was built millions of years ago by one of the most advanced race of the Stargate universe: the Ancients. Five to ten million years ago, due to a plague in the Milky Way Galaxy, they were forced to flee to a planet in the Pegasus Galaxy and there they seeded life on hundreds of worlds as they had done in the Milky Way. After encountering a powerful enemy known as the Wraith and going to war with them for more than one hundred years, the Ancients ultimately lost and were forced to submerge their city beneath Lantea's ocean, which, in the Stargate universe, is the source of the Greek myth of the Lost City of Atlantis.

The city of Atlantis hosts much of the action in the series and is the source of much of the technology which the characters employ. While trying to uncover the secrets the city still holds from her new human inhabitants, the Atlantis expedition also use the Stargate to explore the Pegasus galaxy, looking for energy sources and other technology that the Ancients may have left behind and that may help them defeat the Wraith.

The events of Stargate Atlantis follow the cliffhanger Stargate SG-1 seventh season finale "Lost City", where SG-1 found an outpost made by the race known as the Ancients in Antarctica. After the events of Stargate SG-1 season eight premiere "New Order", the Stargate Command sends an international team to investigate the outpost. Soon, Dr. Jackson discovers the location of the greatest city created by the Ancients, Atlantis.