The Alteran ship was a starship in the Ancient fleet, originally launched from Celestis, designed millions of years ago. It was this vessel that the Ancients used when they fled their home galaxy to avoid the war with the Ori.
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 and buried the evil that had been laid there.
Taken in consideration that this event took place somewhere between 50-100 million years ago, the Alterans, who would later become the faction known as the Ancients (devoted to science and understanding of the universe, in sharp contrast to the religious faction known as the Ori), was already way more advanced than most of the other races in the universe. At the time the Alterans departed Celestis a brilliant scientist named Amelius had created an incredibly powerful device known as "the Ark of Truth". At that time he had also begun working on building the Stargates.
The manner in which the Alteran ship leaves the planet is very similar to the way Atlantis left Earth. Considering the related technology, as well as the large size of the vessel, the Alteran ship is most likely a technological ancestor of the City-ship. (SG1: "The Ark of Truth")
|Capital ships||Alteran ship · Aurora-class · City-ship · Destiny|
|Other ships||Cruiser · Puddle Jumper · Science vessel · Seed ship · Shuttle · Transport ship|