10,000 years ago, when the Ancients attempted to leave the galaxy to the Wraith, one such Ancient, Chaya Sar refused to leave her people, she used her ascended powers to wipe out an entire fleet. As punishment, she was to provide neverending protection to only the people of Proculus.
Over the next 10,000 years, the people lived on Proculus in solitude from other worlds. They also never heard of the Wraith and their power. Athar ensured that everybody was in perfect health, and provided them with enough food and supplies to sustain them. (SGA: "Sanctuary")