P3X-439 is a planet in the Milky Way galaxy, once home to an Ancient colony. Less than a kilometer from the Stargate, a team from Stargate Command found an enormous (and headless, due to its age) colonnade containing a Repository of knowledge at the base.
The Goa'uld Anubis sent a reconnaissance probe to the planet to scout which discovered the secrets the planet held. SG-1, SG-3, and SG-5 arrived first, narrowly preceding the arrival of Anubis's fleet.
Realizing time was of the essence due to the attack, Colonel Jack O'Neill took the drastic step of interfacing with the device, leaving him temporarily incapacitated. As such, Teal'c of Chulak and Dr. Daniel Jackson dragged Jack back to the Stargate while Major Samantha Carter used the detonator to set off some C4, ultimately destroying the repository to prevent it from falling into Anubis's hands.
Anubis later responded by rounding up all the Jaffa who had participated in the battle and having two of his Kull Warriors execute them as punishment while also serving as an example that Anubis himself would not tolerate any kind of failure whatsoever. (SG1: "Lost City, Part 1")