At some point during the Lantean-Wraith war, the Ancients built a device known as the Dolmen on the planet Halcyon. The device would interfere with the higher brain functions of a Wraith and reduce them to a savage state. The Dolmen would keep the Wraith from Culling Halcyon and protect the inhabitants. (SGA: "Halcyon")
Near the end of the Lantean-Wraith war, a hive ship commanded by the Wraith that came to be known as Scar came to the planet of Halcyon at the edge of the Pegasus Galaxy for one final Culling before entering hibernation. Upon arrival, the hive ship and its crew found the Dolmen shielding the population and an Ancient fleet lying in wait. The Dolmen's effect on the Wraith prevented the crew of the hive ship from being able to land and feed and they were forced to remain in space. There, Scar's hive ship engaged in battle with the Ancient fleet and suffered crippling damage, with the hive ship's hyperdrive being damaged beyond repair. However, the Ancient ships didn't fare well either and once the hive ship was crippled, were forced to retreat from the battle, promising to return with reinforcements to finish the job. (SGA: "Halcyon")
With their hyperdrive damaged beyond repair, the hive ship crew are left stranded in space, unable to land due to the effects of the Dolmen and unable to leave. The Ancients also fail to return to destroy them, due to the state of the war at that point. With the crew going insane with rage and hunger, they ultimately decided to enter stasis and landed the hive ship on Halcyon on automatic, launching a marker satellite to act as a distress beacon to the other Wraith once they awoke. There, the ship lay for millennia, long enough that a hillside grew up around it.
The derelict hive ship was eventually rediscovered by the people of the Fourth Dynast. Due to the Dolmen, the people of Halcyon were able to enslave Wraith as soldiers and by waking the Wraith aboard the hive ship, the people of the Fourth Dynast had a greater army than that of anyone else who had to capture their Wraith off-world. Due to the experiments that were done upon the hive ship by the scientist Kelfer, Scar was able to escape and retained his sentience. Scar activated the marker satellite before being captured and put into the Fourth Dynast's hunting enclosure after he proved to be uncontrollable. The Wraith also began coming out of stasis in greater numbers due to the awakening of all the Wraith following the death of the Wraith Keeper.
Looking for allies, the First Atlantis Reconnaissance Team visited Halcyon where they discovered the marker satellite and destroyed it before it could broadcast information on Halcyon to the other Wraith. They eventually learned of the hive ship and Scar who forced Lieutenant Colonel John Sheppard to destroy the Dolmen, awakening the hive ship fully once more. Scar attempted to take the hive ship into orbit and lead a brutal Culling, but used a self-destruct program created by Kelfer to destroy his own hive ship after he was mortally wounded. Scar's hive ship and its Wraith crew were destroyed in the explosion, but Sheppard's team and the surviving Halcyionites onboard were rescued by the Daedalus Asgard transporters before the explosion. (SGA: "Halcyon")