A Prior of the Ori came to the planet Kallana to convert its inhabitants to Origin. But the Jaffa of the planet, having previously worshiped the Goa'uld refused to follow the teachings of the Book of Origin and they were struck down by the Prior, resulting in their deaths. Soon afterwards, a mysterious blue forcefield appeared around the Prior and the Stargate. The Goa'uld Nerus contacted Stargate Command and informed them of the situation and that when the forcefield expands it weakens enough to be penetrated with Asgard transporters. (SG1: "Beachhead")