When Stargate SG-1 was finishing up its sixth season, the show’s writers did not expect that the SCI FI Channel would be ordering a seventh … and then an eighth, a ninth, and a tenth! The plan was to follow Anubis’s big coming out party in “Full Circle” with a theatrical movie for the SG-1 team, which in turn would set up a spin-off series to continue in SG-1’s time slot: Stargate Atlantis.

The story that eventually became the seventh season finale — the fan-favorite “Lost City” — actually started out life as that movie pitch.

“We pitched it to MGM as a movie,” Robert C. Cooper tells “Dial the Gate” in a brand new interview. Cooper was a writer and executive producer on the franchise, and co-created Atlantis with Brad Wright. He said that the big reveal of the city of Atlantis that was the image taken in for the pitch. “What if the lost city of Atlantis was an alien space ship that then rose up out of the ocean, as our big set piece? And originally it was on Earth — it was not in the Pegasus Galaxy.”

In this Saturday’s interview Cooper talks with “Dial the Gate” host David Read about this important piece of Stargate history — making changes to “Lost City,” figuring out how to produce two shows at the same time, and the benefits of moving the spin-off to an entirely new corner of the Stargate universe.

Watch this exclusive clip from the conversation:

By the time Stargate SG-1 reached the end of its seventh season, plans were in motion for Atlantis as a spin-off series. “Lost City” was to set this up, complete with the discovery of the city itself under the ice of Antarctica … and then the parent show would end.

The adventures of the SG-1 team would continue on the big screen, while the city of Atlantis took over for the S.G.C. as the center of gate operations for Earth.

It was then SCI FI President Bonnie Hammer who asked for both shows to air concurrently, Cooper said.

“We pitched the whole thing out to her,” with “Lost City” as the transition to Atlantis, he said. “… And she was like, ‘Oh no no, we’re going to do both!’ And that was the first time we heard that. We had talked all about essentially ending SG-1 at the end of Season Seven. Rick [Richard Dean Anderson] had been talking about ‘time to move on’ and ‘enough of O’Neill’ and that type of thing.”

Keeping Anderson on a part-time basis meant promoting Jack O’Neill to Brigadier General for the eighth season. And putting the spin-off on the air while SG-1 and Stargate Command were still running around the Milky Way Galaxy saving the day meant moving the lost city of the Ancients to a different galaxy altogether.

The city’s departure from Earth was originally scripted as the final shot in “Lost City,” after Jack is frozen in a stasis pod — even including a shot of the Ancient woman Ayiana (“Frozen”) in her own stasis pod. Wright and Cooper ended up cutting this scene and moving it to the opening moments of the Atlantis pilot.

“Atlantis needed to stand alone from SG-1,” Cooper said. “We wanted Atlantis to be a fresh, new adventure without the baggage of SG-1 — without going, ‘Where are the Goa’uld?’ and all that stuff. ‘And the Replicators?’ So we wanted to start with a clean slate. And the best way to do that was to start fresh in a new galaxy.”

Don’t miss the full conversation with Robert C. Cooper this Saturday, July 29, starting at 1 p.m Pacific time (4 p.m. Eastern, 9 p.m. BST) on “Dial the Gate!” While you’re there also subscribe to GateWorld’s YouTube channel for more clips like this, plus original Stargate goodness coming soon.