Kallana was a planet in the Milky Way galaxy, which held a Stargate and was under the jurisdiction of Jaffa, formerly loyal to Cronus. The planet was chosen by the Ori to be the location of a Supergate that would serve as a beach head for an Ori Crusade into the Milky Way.
A Prior arrived on Kallana, however after the Jaffa inhabitants rejected Origin the prior created a force field around the planet's Stargate. Leaching off energy from attacks by both the Free Jaffa Nation and the Tau'ri, the force field rapidly engulfed the entire planet and compressed it into a singularity as to create a permanent power source for a Supergate.
The Supergate was later destroyed by Vala Mal Doran after she disrupted the gate's construction process before it was able to be activated although Kallana had already been destroyed. (SG1: "Beachhead")