The Ancients, one of the four great races of the Ancient Alliance, were the builders of the stargates. The Ancients had evolved from a race of humans that lived long before us, but they were wiped out by a plague that was sweeping across the galaxy. Many learned to ascend and became the energy beings known as the Others, and the rest died out. A device of Ancient design on the planet Dakara uses an energy wave to reduce all matter to its basic molecular elements, and the device was used by the surviving Ancients to begin a second evolution and to recreate life in the Milky Way Galaxy following the plague.

Evidence suggesting the presence of the Ancients on Earth was uncovered when Ayiana was discovered and revived in Antarctica. Tests revealed that she predated human evolution on Earth by 50 million years, suggesting that she was a living Ancient, or an example of an advanced stage of the potential human evolutionary process leading to the development of the Ancients. Although the Ancients moved on from their region of space long ago, they have left behind artifacts and ruins scattered across the galaxies. On P3R-272, SG-1 found a repository of the Ancients, a device that is an archive of Ancient knowledge. It downloaded an alien database into O'Neill's brain, giving him the ability to speak the Ancient language and to enter programming into the SGC computer to identify new stargates not known on the Abydos cartouche. Among these was P9Q-281, a deserted planet that has a pedestal near the gate with symbols matching the language of the Ancients. Technology of the Ancients also created the device on P4X-639, intended as a time machine to go back and change history to avoid a catastrophic fate, but which instead caused a short term continuous time loop. An Ancient reanimation device, designed for healing but used by the Goa'uld Telchak as the basis for the technology of the sarcophagus, was found on Earth. Technology encountered on other worlds, including Anubis's weapon which caused the destruction of one stargate by another, the DNA resequencer of P3X-367, the inter-dimensional device of P9X-391, the small stone found on P3R-233 which acted as a psychic communication device, the transportation obelisk on P9G-844 which the Sodan referred to as the Eye of the Gods, and the Sodan personal cloak of invisibility, were also of Ancient design. Ancient texts also refer to a legendary treasure that has eluded SG-1, the Clava Thessara Infinitas, or Key to Infinite Treasure, which, according to legend, will allow he who possesses it entry to a vast cache of wealth and weapons hidden away by the Ancients prior to their ascension.

Some pieces of Ancient technology can only be activated by a user who possesses a specific Ancient gene. O'Neill possesses the gene, which may have accounted for his ability to access the knowledge of the Ancient repository. When SG-1 visited the world where Maybourne ruled as King Arkhan, they discovered an abandoned Ancient spacecraft which responded to the Ancient gene in O'Neill, allowing him to fly it through the control of his mind. The ship also contained a time travel device, and written records on the planet suggested the first evidence that the Ancients had mastered time travel. Both the device and the ship were recovered by SG-1.

A tablet found in a secret chamber in the catacombs of Ra's pyramid on Abydos, written in one of the oldest dialects of the Ancients, revealed the existence of a Lost City of the Ancients which holds the key to powerful Ancient weapons and technology. SG-1 came a step closer to finding the Lost City when a second repository of the Ancients was discovered on P3X-439, and O'Neill once again interfaced with the device and acquired the Ancient knowledge. Using the knowledge of the Ancients, the search across the galaxy for the Lost City and its secrets led SG-1 first to Praclarush Taonas, a world now lost in fire and lava flows, then back to Earth and a small Ancient outpost now buried beneath the ice of Antarctica. There, the Ancient gene within O'Neill allowed him to harness the power of Ancient technology, including the zero point module power source and the Ancient defense weapons platform which released swarms of energy drones, to defeat Anubis and to save Earth. Although the structure beneath the ice was only a small Ancient outpost, it provided the key to finally finding the Lost City of the Ancients - Atlantis. A subsequent scientific expedition to the Pegasus Galaxy under the command of Dr. Elizabeth Weir led to the discovery of the Lost City of Atlantis and of a wealth of Ancient knowledge and technology.

On Earth, SG-1 discovered a series of caverns deep below Glastonbury Tor which contained not only transporter rings, holograms, riddles, and writings of the Ancients, but also revealed a vast treasure of gold and jewels, a magnificent Ancient text, and a terminal device which, in conjunction with the Ancient communication stones, is capable of intergalactic communication. It was from the database in Atlantis and from the Ancient text from the caves of Glastonbury that the clues to the earliest origins of the Ancients were at last revealed. Millennia ago, in a distant galaxy, a race called the Alterans were a human society on an evolutionary path to ascension. However, a philosophical division grew. Some grew more and more fervent in their religious belief, while others believed in science and free will. Rather than go to war, many Alterans built a ship and went on a great journey through space, leaving their galaxy behind and eventually settling in the Milky Way Galaxy. They named their new home Avalon, and they became known as the Ancients, the most powerful race to ever inhabit the galaxy. Those they had left behind came to be known as the Ori, who eventually ascended and passed down a religion called Origin to the next evolution of humans they created.

The Ancients built stargates and colonized the galaxy, then eventually left our galaxy to settle in the Pegasus Galaxy where they established the city of Atlantis. The Lantian civilization flourished in the Pegasus Galaxy, but there they encountered the Wraith, an alien species that feeds on humans by drawing the life force from them. Besieged by the Wraith, the Lantian Ancients abandoned Atlantis and left the Pegasus Galaxy more than 10,000 years ago to return to the Milky Way. Praclarush Taonas was one of the earliest Lantian cities, but it was abandoned when the inhabitants learned that their sun was nearing the end of its life. Many Lantians, among them Merlin and Morgan Le Fay, returned to Earth, but Earth was then a harsh and primitive place. There was no hope of living among the primitive people as Lantians or of rebuilding their society, so instead they spread out to many lands, some planting a few small seeds of civilization among the first tribes of man, others making their way to the stargate in Antarctica to leave the planet, and still others choosing to live the remainder of their lives in seclusion and meditation. Through physical and mental evolution, some Ancients found a way to shed their physical bodies and to ascend to live as energy on a higher plane of existence. When the plague swept through the galaxy, threatening to wipe out the Ancients, many survived by learning to ascend, and the surviving Ancients began the second evolution to recreate life in the galaxy.

As ascended beings, the Ancients realized that the temptation to manipulate and align lower life forms in some order for one's own purposes could result in disastrously abusive corruption, and they believe so strongly in free will that their highest law forbids their intervention in the affairs of the lower planes, even if it were to mean the destruction of an entire galaxy. However they understood the threat posed by the Ori, who draw their power from the worship of others and who require that all unbelievers be destroyed, and through the ages the Ancients have protected life in this galaxy by shielding the very existence of our galaxy from the Ori. Both Merlin and Morgan Le Fay had chosen the path of seclusion, meditation, and ascension, however, thousands of years later, recognizing the threat that the Ori could one day become, Merlin retook his human form in order to create a weapon capable of destroying ascended beings. In doing so, Merlin had broken the highest laws, and the Ancients, fearing his intentions, sent Morgan Le Fay to stop him. As ascended beings, the Ori themselves cannot act in this galaxy without incurring the interference of the Ancients, but as the Ori learned of the existence of the Milky Way Galaxy and set about increasing their power by sending their human armies to conquer new worlds of followers, the Ancients took no action against them. A few, however, including Merlin, Morgan Le Fay, and Orlin, were permitted limited cooperation with SG-1 in facing the invasion of the galaxy by the armies of the Ori. The final outcome hangs in the balance, for the Ori are coming to destroy the Ancients.

Cross Reference: Alterans, Ancient Alliance, Ancient Communication Stone, Ancient Communication Terminal, Ancient Control Console, Ancient Defense Weapon, Ancient Gene, Ancient Language, Ancient Outpost, Ancient Repository, Ancient Spacecraft, Ancient Stasis Chamber, Ancient Tablet, Ancient Time Travel Device, Ancient Transporter, Antarctica, Anubis, Anubis's Ancient Weapon, King Arkhan, Ascension, Atlantis, Avalon, Ayiana, Clava Thessara Infinitas, Dakara, Dakara Weapon, Disruptor, DNA Resequencer, Earth, Energy Generator, Eye of the Gods, Fifth Race, Glastonbury, Holographic Projection, Inter-Dimensional Device, Invisibility, Lost City, Merlin, Merlin's Treasure, Merlin's Weapon, Morgan Le Fay, Oma Desala, Ori, Orlin, Others, P3R-272, P3X-439, P4X-639, P9G-844, P9Q-281, P9X-391, Pegasus Galaxy, Praclarush Taonas, Reanimation Device, Sodan, Sodan Cloak, Stargate, Time Loop, Vis Uban, Wraith, Zero Point Module

Episode Reference: The Fifth Race, Frozen, Full Circle, Lost City, Threads, Avalon, The Fourth Horseman, The Pegasus Project