- "Is forced indoctrination really the answer? You would deny the Ori the very essence of self."
The Ark is able to show anyone the "truth" which is programmed into the device, which makes it essentially a brainwashing device. To activate the device, someone has to type in the programmed password into the control device on top of the Ark. If the password is correct, the red crystal on top of the device would light up. If the Ark would be opened now, a blinding beam of light would come from it and affect anybody in the vicinity. Vala Mal Doran speculates that the Ark could only make people believe things that were true, based on Adria's comments that she could not use the Ark to brainwash people into following the teaching of Origin, suggesting that it projects the truth based on evidence that has been programmed into it. (SG1: "The Ark of Truth")
When the Alterans were trying to find a way to counter the growing threat of the Ori and their followers, the scientist Amelius designed the Ark as a way to even the odds. However, the other Alterans believed that such a device denied the Ori their right to free will. It was decided that the Ark would not be used, and was left in Ortus Mallum when the Alterans fled in their ship.
Millions of years later, Morgan Le Fay began sending Dr. Daniel Jackson visions of the Ark and the destruction of Ortus Mallum, posing as Merlin during these visions to conceal her identity. Heading for the Alteran Home Galaxy, SG-1 searched the ruins of the village and found the Ark in the tunnels that it was hidden in. The Ori army ambushed them, taking the Ark to the City of Celestis. Adria explained to Vala Mal Doran that she had decided not to use it, feeling that people needed to see her for what she was, as well as the belief it generated not providing her with the right kind of energy that she needed to increase her strength.However, Morgan showed the necessary activation symbols to Vala, and told Daniel that he needed to expose it to a single Prior; the subspace link between the crystals in the Prior's staffs would thus transfer the programmed "truth" to all other Priors in the galaxy. When Adria again confronted them, Daniel typed in the necessary code, realizing that the password was "Origin", and exposed it to the Doci, who also transmitted it to the other Priors. With her power weakened, Adria was attacked by Morgan, and the two engaged in eternal battle.
Taking the Ark back to Earth, the Tau'ri showed it to another Prior, who also transmitted it through his staff to the other Priors in the Milky Way, ending the Ori crusade. Daniel Jackson advocated that the Ark be destroyed, saying that it was too risky to keep, but the International Oversight Advisory decided that the Ark would be studied at Area 51. (SG1: "The Ark of Truth")