P3R-272 is an apparently uninhabited world. The stargate is housed in a sealed chamber, and an inscription on the floor reads, "Noo Ani Anqueetus" ("We are the Ancients"), and "Hic Qua Videeum" ("The Place of Our Legacy"). An alien device on the chamber wall is an Ancient repository, an archive of the knowledge of the Ancients. When O'Neill peered into the device, it activated and downloaded an alien language and database into his brain.
Episode Reference: The Fifth Race