Dagan, formerly known as Sudaria, was a planet in the Pegasus galaxy. When the Lanteans fled Atlantis after they lost the war with the Wraith, one of them left a Zero Point Module with the Quindosium, members of an order which belonged to the Sudarian society that worshiped the Ancients. Unfortunately, ten thousand years of cullings left the Sudarian society extinct, while the modern Daganians were at a renaissance level of technology. However, there was a portion of the population who still followed the ways of the Quindosium and worshiped the Ancestors.
Sudaria, ten thousand years ago.
After an alternate Elizabeth Weir was awoken from her stasis pod and supplied a list of planets with ZPMs to the Atlantis expedition, the First Atlantis Reconnaissance Team traveled to Dagan and eventually located the ZPM, however the new members of the Quindosium took it from them, hoping that the actual Ancients would one day return for it. (SGA: "The Brotherhood")