An Alpha Site is an offworld base operated by the Tau'ri, generally, as per its designation, the primary such.
The Alpha Site was originally established to serve two main purposes:
- Contingency base: in the case of an overwhelming Goa'uld attack on Earth (a very real possibility during the Stargate Program's first years in operation), the heads of Earth's governments and other key personnel would be evacuated to this off-world base, where they could organize a resistance or, in the worst case, preserve a remnant of the human race
- Quarantine: if SG teams want to bring artifacts or other samples back to Earth or if a teammember acquires some pathogen off-world, these can be quarantined at the Alpha Site without risk of exposing Earth to unknown technology or biota
As the Tau'ri presence in the galaxy and their engagement in the fight against the Goa'uld increased, Alpha Sites were also used to train and coordinate allied forces such as Free Jaffa and the Tok'ra, stockpile materiel, and develop prototype technologies.