The Tok'ra's base on a planet in the Risa System was discovered and attacked by Anubis. SG personnel and the Tok'ra evacuated to the Alpha Site. The Risa Base was destroyed by the Tok'ra to prevent the discovery of the Stargate address of the Alpha Site. (6.09 "Allegiance")
Anubis was determined to wipe out the Tok'ra and when he discovered their base in the Risa System, he sent a large attack force, as well as an Ashrak, to destroy them. SG-12 and SG-15 were also on the base to help the Tok'ra evacuate, but all members of SG-12 perished in the first wave of the attack. Surviving Tok'ra and SG-15, under the command of Pierce, evacuated to the Alpha Site. Dr. Janet Fraiser was positioned right at the Stargate at the Alpha Site to triage the victims, aided by SG personnel as well as Rebel Jaffa who had also taken refuge there when their own base of operations had been destroyed by the Goa'uld a few months prior.
Jacob Carter/Selmak dialed the Alpha Site on the Risa DHD. To make sure that the Stargate address of the Alpha Site remained a secret, he stayed behind long enough to set a charge that was equivalent to a tactical nuclear weapon and that was on a ten-second delay to allow everyone to leave. In all probability, the resulting explosion destroyed the Stargate at the Risa Base as well.
Anubis' attack on the base killed over three-fourths of the Tok'ra, a very serious blow to their already quickly dwindling number. The Ashrak who came through the Stargate with the evacuees while under an invisibility cloak killed two Tok'ra (including the Risa Base leader Ocker), two Rebel Jaffa, and one Tau'ri before he himself was discovered and killed.
--DeeKayP 18:56, 30 April 2010 (UTC)