Mass Relays are mass transit devices scattered throughout the galaxy, usually located within star systems. They form an enormous network allowing interstellar travel. Hailed as one of the greatest achievements, a mass relay can transport starships instantaneously to another relay within the network, allowing for journeys that would otherwise take years or even decades with only FTL drives.
The Stargates, also called the Astria Porta in Ancient, are a series of devices, built by the Ancients, that create artificial subspace wormholes, allowing for near-instantaneous transportation between two distant points in space. The Stargates are often considered to be the Ancients' greatest creation, and so the Ancients are often called the Gate Builders. The Ancients, the Asurans, the Tollan, and the Givosions are the only known races that have managed to build Stargates.
The original Stargate design was invented by an Alteran named Amelius, from an idea he formulated the night before the Alterans left their home galaxy for the Milky Way. It is unknown if he actually built the first of the Stargate Network. They are among the oldest examples of Ancient technology found in the Milky Way galaxy; the Stargate found in Antarctica on Earth has been estimated to be over 50 million years old.
The original Stargate design was invented by an Alteran named Amelius, from an idea he formulated the night before the Alterans left their home galaxy for the Milky Way. It is unknown if he actually built the first of the Stargate Network. They are among the oldest examples of Ancient technology found in the Milky Way galaxy; the Stargate found in Antarctica on Earth has been estimated to be over 50 million years old.