This season finale, The Lost City part 1, is also rumored to be the lead-in to the spin-off "Stargate: Atlantis" series.

While off-planet SG-1 discovers another of those Ancients' information devices that once filled Jack's head with knowledge.
The Goa'uld arrive.
Jack puts his head in the machine to gain information before SG-1 destroys it to keep it from the Goa'uld.
The President replaces General Hammond with Dr. Theresa Weir and SG-1 learns that Anubis is heading towards Earth to gain SG-1's knowledge of the Ancients and to conquer Earth.
SG-1 heads off-world in an attempt to find the Lost City, gain Ancient technology to defeat Anubis, and to help Jack before he overloads and dies.
Anubis’s ships descend on DC.
Off-world, the knowledge in Jack's head helps him to identify the location of the Lost City
- it's back on Earth, in the Antarctic, where the 2nd Gate was found in the episode "Solitudes" and the frozen Ancient, Ayiana, was found in the episode "Frozen."
The Ancients, their technology and the rising of Atlantis.