STARGATE ATLANTIS SEASON ONE  SANCTUARY EPISODE 114

McKay has swiped a Z.P.M. that defended a world from the Wraith before ("Childhood's End") -- thus his insistance that he has no intention of stealing Proculus's Z.P.M., should they have one.Including both the expedition from Earth and the Athosians living on the mainland, Atlantis's planet includes about 200 inhabitants. The expedition members are currently living in just one part of the city, because they do not have the ability to power the entire city with the naquadah generators brought from Earth.Chaya appears to recognize the name "Earth" when Major Sheppard tells her where they are from.
Chaya herself is Athar, an ascended Ancient who lived on Proculus when she was a mortal -- implying that Proculus itself may have been an Ancient colony. Or, perhaps the Atlanteans sent people to live on the planets they seeded with human life, to monitor their development. During this time she ascended; then, when the Wraith first came to Proculus, she lashed out with her mind and destroyed them to keep her people safe.
It is thus likely that the Wraith did not evolve to a point where they became a significant threat to the human population of the Pegasus Galaxy until after some of the Ancients ascended.

Chaya / Athar is the first evidence we have seen of an ascended Ancient in the Pegasus Galaxy. When in their evolution the Ancients first discovered ascension remains a mystery, but it appears that when they did, not all of them ascended. Those in Pegasus who did ascend did not destroy the Wraith; those who did not ascend eventually fled back through the Stargate to Earth when the Wraith beseiged Atlantis ("Rising, Part 1").
Those Ancients who ascended obviously adopted a radically different philosophy, particularly the highest rule that they not interfere with the concerns of mortal life. They likely even left their own kind, the unascended Ancients, at the mercy of the Wraith.An ascended Ancient can travel freely through the vacuum of space: Athar gated directly back to the Proculus Stargate in orbit of the planet. Ascended Ancients have great control over the weather and electricity, as Oma Desala demonstrated when she destroyed Apophis's army in SG-1's "Maternal Instinct." They can even lash out with a powerful electromagnetic blast beyond the atmosphere of a planet.