Alteran ship

The Alteran ship was the vessel that the Ancients used when they fled their home galaxy to avoid the war with the Ori.

History
Built inside the mountain that Ortus Mallum was located on, the ship's departure devastated the mountain and buried the village, but the tunnels where the Ancients hid their technology were preserved.

The Ori would claim this as a victory, and would later build the City of Celestis near the mountain. In the Book of Origin, they said that the mountain erupted buried the evil that had been laid their.

Behind the scenes
The manner in which the Alteran ship leaves the planet is very similar to the way Atlantis left Earth in Rising. Considering the related technology, the Alteran ship may infact be a technological ancestor of the city-ship.