While the characters in early episodes of Stargate SG-1 often referred to a group of mysterious aliens by using terms like "the gate-builders", I believe the first time those aliens were referred to as "the Ancients" was in S2E16 "The Fifth Race" in 1998. As far as I can tell, the first time the Ancients were brought up on Farscape was S1E16 "A Human Reaction" in 1999. Even if you assume the idea was planned from the very beginning of Farscape, the first episode still aired in 1999, months after the Ancients had been established in Stargate.

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