Lantean

"Why'd they leave? Um, who knows? We know the Ancients on Earth were suffering from a plague. Uh, maybe some of them were trying to start over, seeding life in a new galaxy."

- Daniel Jackson The Lanteans, also known as the Ancestors, were those Ancients who left Earth in the City-ship and settled in the Pegasus galaxy. They were directly responsible for the emergence of the Asurans and the Wraith.

Generally, the term "Lantean" is used to describe Alterans who inhabited though it can also refer to any Ancient who lived in the Pegasus galaxy at the time of Atlantis.

Arrival
"... in the hope of spreading new life in a galaxy where there appeared to be none. Soon the new life grew, prospered...In time, a thousand worlds bore the fruit of life in this form."

- Melia After leaving the Milky Way roughly 5-10 million years ago and arriving in the Pegasus galaxy, the Ancients settled on a planet named Lantea, and came to be known as the Lanteans. Finding Pegasus devoid of sentient life, the Lanteans seeded Pegasus with baseline Humans, who would come to call them the Ancestors.

The great enemy
"The Lanteans were powerful but careless."

- Todd

However, one of the planets seeded held a creature called the Iratus bug, which began feeding off the Humans seeded there. Eventually, the bug|Iratus bugs began to mutate, taking on advantageous human characteristics. This resulted in a hybrid species, the. For over a century, the Lanteans and the Wraith were at war with each other.

While at first the Lanteans had the advantage of technological superiority and were close to defeating the Wraith, their carelessness allowed the Wraith to capture Zero Point Modules from several of their warships at great cost to themselves, which they then used to power a cloning facility allowing their numbers to grow a hundredfold. The Lanteans' near-indestructible ships allowed them to win almost every battle they fought, but the Wraith just kept coming. The tables were turned and the Lanteans began to lose both warships and territory. Desperate, they turned to extreme measures, such as Project Arcturus, an attempt to extract point Zero point energy from their own universe, a nanovirus, and its successor the replicators. These projects failed with disastrous and far reaching consequences. By then, the Lanteans were losing the war, and they knew it, so they sank their capital city,, into the ocean.

In a final attempt at ending the war, the Lanteans sent a delegation to meet with the Wraith to negotiate a truce. The Lantean delegation was protected by their most powerful warships, but they were ambushed by the Wraith's massive fleet and destroyed. Seeing no way to win, and every moral solution exhausted, the few remaining Lanteans returned to  via  hoping to one day return, leaving Pegasus and her denizens at the mercy of the Wraith until the  came through from the Milky Way 10,000 years later.

Twilight
"When we first abandoned Atlantis all those millennia ago, the Earth was so harsh, its people so primitive by comparison, there was no hope of living among them as Lanteans or rebuilding our society. So instead we spread out to many lands, some of us planting a few small seeds of civilization among the first tribes of man, others making their way to the Stargate at your southern pole. Still others choosing to live the remainder of our lives in seclusion and meditation."

- Ganos Lal Upon arriving at Earth, they quickly realized that there was no hope of rebuilding their society, as Earth was too harsh and the s there too primitive. Some chose to go to other worlds, others, and some chose to join the native humans, where they integrated into human society (which is how several humans came to possess a specific gene required to use Ancient technology.

The Ancients that left Earth were later part of the Alliance of Four Great Races, with the Asgard, the Furlings, and the Nox. It was after their return to Earth that they developed some of their most advanced technology, including: beam transporters with the ability to beam entire structures through a Stargate, Molecular construction devices (used to build anything at the molecular level using one's mind), solid holograms (which could physically interact with matter).

Legacy
The Lanteans were worshiped as gods by the people of the Pegasus galaxy and some of their technology was left behind to be found and used by people who understood it. Atlantis was among the many wonders left behind and was ultimately discovered by the Atlantis expedition who moved into the abandoned city and used it as their base of operations in the Pegasus Galaxy. A lot of technology was left behind in the city itself. Also several outposts still existed along with at least a few Zero Point Modules. The enemy they inadvertently created, the Wraith, still existed, as well as the Asurans, whom the Lanteans had previously attempted to destroy. The Asurans replicated themselves into the billions and established a large civilization and city on their homeworld. When the Atlantis expedition encountered them, they altered the Asuran base code to reactivate the Wraith attack command. This resulted in them finding a new strategy to devastate human worlds to starve the Wraith. Eventually, their homeworld was destroyed by an allied fleet of the Tau'ri, Wraith, and Travelers and resulted in the final destruction of the Asurans. It was the Lanteans that passed on the story of the city that sank into the sea to the Greeks

Architecture
After traveling to the Pegasus Galaxy, the Ancients built structures of metal, and they were quite large. Atlantis, the centerpiece of their society, was a massive City-Ship capable of space travel. They built many other ships, but most were destroyed during the war with the Wraith. Their technology also appeared more advanced, made of metal instead of stone; it was also digital, like the symbols on the Stargates in the Pegasus Galaxy, and utilized crystals in their consoles instead of stone tablets. They also kept their archives in computers instead of downloading the knowledge directly into a person's mind.