An ancient site beyond the containment dome on P3X-289, located within the region of Mahg Mar. The inhabitants of the dome believed it to be the location of ancient ruins from the time of the Goa'uld System Lord Morrigan's reign over the planet. It was also the original location of the Stargate, or "Gate of Mahg Mar," until it was taken and put on display in the National Museum of History.
It is likely that Morrigan had a temple or some other kind of Goa'uld remains amidst the ruins at Danaan, where the people were able to learn her name many generations later.
Revisions - SG-1 learns of Danaan from the suviving inhabitants of P3X-289, who live in a bio-dome amidst the toxic environment.