Supergate

Massive Stargate developed by the Ori, spanning three to four hundred meters across. Comprised of 80 individual segments, the device draws its power from a black hole, the only force in the universe strong enough to sustain it indefinitely.

The Supergate was developed for the specific purpose of establishing permanent footholds in distant locations in the universe, permitting one-way passage of enormous Ori warships.

The only known defense against the Supergate is to break the chain of connecting segments, causing a power surge that prevents the completion of the device.

KEY EPISODES

Beachhead - Once the Ori force field encompasses Kallana, Supergate components begin to arrive and come together to create the massive Stargate.
Camelot - A second Supergate is discovered in the Milky Way, and it is not long before it opens to admit four bloodthirsty Ori ships into the galaxy.
The Pegasus Project - SG-1 initiates a plan to indefinitely place a busy signal on the Ori Supergate, by dialing it from the Pegasus Galaxy.
The Shroud - Daniel, now a Prior, pleads with SG-1 to sever the connection blocking the Ori Supergate. Once down, he pilots an Ori ship back to the Ori galaxy and uses Merlin's weapon to kill the ascended beings who live there.
Stargate: The Ark of Truth - SG-1 takes the Odyssey through the supergate to the Ori galaxy in a last-ditch effort to stop the forces of Origin once and for all.