The Ancient tablet found on Abydos described a Lost City of the Ancients which holds powerful Ancient technology and weapons. Hoping that these weapons would enable Earth to defeat Anubis, SG-1 struggled to translate the Ancient text and find the mythical Lost City.
Early errors in the translation suggested that the Lost City was really the City of the Lost, possibly the ancient city of Vis Uban. Later interpretations suggested that the Lost City had been given its name because it had been made lost, hidden from those who might try to find it, with all reference to it removed from the written history.
The knowledge of the Ancient repository on P3X-439, which was downloaded into O'Neill's mind, led SG-1 to Praclarush Taonas in search of the Lost City. There a holographic map at least 30 million years old suggested that the answer lay beneath the ice of Antarctica. In Antarctica, SG-1 found an Ancient outpost with powerful weapons that defeated Anubis and his fleet, but the site was too small to have been the Lost City they sought. However, later research at the outpost did eventually lead to the discovery of the Lost City of Atlantis in the Pegasus Galaxy.
Cross Reference: Ancients, Ancient Outpost, Ancient Tablet, Antarctica, Atlantis, Praclarush Taonas, Vis Uban
Episode Reference: Full Circle, Fallen, Lost City