Erebus was a planet in the Milky Way galaxy used for the construction of Goa'uld Ha'tak vessels, and the location of a Jaffa labor camp for those forced into their construction. Erebus also includes facilities for the purification of the Naquadah required to build the ships. Only Jaffa labor is used, as only they can withstand the temperatures and toxic gasses emitted by the blast furnaces fed by underground volcanic systems.
Captured enemy Jaffa are sent to work themselves to death on this desolate planet with sparse vegetation. Many are prisoners of war who are unwilling to serve their new Goa'uld masters. The planet was recently captured by the System Lord Ba'al. A forcefield defends the Stargate on Erebus, much like an iris. The workers are guarded by Jaffa in the service of Ba'al, who are overseen by the Erebus Commander. When slaves become too weak to make their work quotas, they are taken out in front of the encampment and publicly executed, presumably by Jaffa Guards wielding staff weapons.
Known in Greek mythology as the place where condemned souls pass as soon as they die, Erebus is considered one of the first levels of hell. Dr. Daniel Jackson once visited the planet as an ascended being, but could only watch the torment of the Jaffa, powerless to interfere because of the rules of the Ancients. When he returned to human form and rejoined SG-1, he led the team to the planet where Teal'c's son Rya'c and mentor Bra'tac were held prisoner -- captured during an apparent attempt to liberate the camp and win recruits to the Jaffa Rebellion. Erebus's slave encampment was liberated by SG-1, SG-2 and SG-3 with all of its prisoners eventually being relocated to the Alpha Site, anxious to join the Jaffa Rebellion. (SG1: "Orpheus")