Janus' outpost was a planet in the Milky Way galaxy which has a Stargate. For ten thousand years ago placed Ancient scientist Janus an outpost on the planet. He placed his time travel technology. In the future, had Tau'ri found the outpost and found Janus' technology. They locked the planet Stargate so Stargate Command in the current timeline would not come to the planet. (SG1: "Relativity")