Merlin believed that the Ori represented a significant threat to the safety of this galaxy and to the Ancients themselves, who refused to take any action to protect themselves against them. So great was his fear that he retook human form and developed a weapon capable of destroying ascended beings, and he created a phase-shift device for the sole purpose of shifting his research into another dimension to conceal his work from the Others. Merlin's device was not a weapon in the conventional sense since ascended beings transcend ordinary space-time as we know it, so a "weapon" used against them would have to do the same thing. Instead, the weapon was an energy transfer device similar to a zero point module, except that the energy is channeled not from subspace into ordinary space-time, but rather into the dimension occupied by ascended beings. The energy is a form of interference that doesn't kill, but rather neutralizes, a simple analogy being two standing waves canceling each other out.
Merlin's log indicated that he had completed the device on Earth but had had to relocate it to another planet, the coordinates of which matched PX1-767, the world of Camelot. SG-1 sought the weapon as their best hope to defeat the Ori, but in Camelot they learned that the Sangreal, the Holy Grail that is the key to the weapon, was no longer there. Their quest took them to Castiana, Sahal, and Vagon Brei, then finally to a planet, the address of which was a combination of the symbols for those three worlds. There SG-1 passed a series of challenges put in place by Morgan Le Fay as safeguards to ensure that the Sangreal and Merlin's weapon could only be claimed by those possessing truth of spirit.
At last SG-1 came to Merlin's cave where Merlin himself had been suspended in stasis by Morgan Le Fay, who had destroyed the weapon to protect it from the Ancients and then had preserved the one man capable of building another. Merlin was revived, and recognizing the imminent threat presented by the Ori, he agreed to rebuild his device. Using an Ancient repository, Merlin pieced the device together using virtual components created from base molecules. As each holographic component was designed and configured virtually, the pieces merged and took shape, then materialized into solid form. The red jewel of the Sangreal would be the final component, the key to making it work. Merlin knew that his body had deteriorated too much during stasis and he would be unable to finish the job. Instead he uploaded some of this knowledge into the Ancient repository so that when Daniel interfaced with it, he acquired the knowledge and the ability to complete the task. However, Daniel had only completed the first two stages when he and the device were captured by Adria.
Adria intended to use Merlin's weapon to wipe out the Ancients in this galaxy, but she feared interference from the Ancients and she relied on Daniel to complete the device. Daniel agreed to help her and continued to develop the weapon as part of a complex deception that would turn the weapon against the Ori. Using Daniel's directions, Vala completed the final components and added the red Sangreal stone, which was held suspended above the device and glowed when it was ready to be activated with the timing crystal. The Sangreal completed Merlin's weapon, and when the timing crystal was replaced, the power crystals at its center began to glow in a pulsing rhythm. The device was armed and sent on an Ori warship through the supergate to the Ori galaxy, however there was no way to determine if the weapon had successfully destroyed the Ori.
Cross Reference: Adria, Ancients, Ancient Repository, Camelot, Castiana, Crystals, Holographic Projection, Merlin, Merlin's Cave, Merlin's Library, Merlin's Phase-Shift Device, Morgan Le Fay, Ori, PX1-767, Sahal, Sangreal, Sangreal Planet, Supergate, Vagon Brei
Episode Reference: Arthur's Mantle, Camelot, The Quest, The Shroud