The Defensive Perimeter existed around the edge of Fortress Inquisitorius, which itself was situated on the ocean moon of Nur within the Mustafar system. Specifically, Airlock 8 could be found as a part of the Defensive Perimeter.
In 14 BBY, as part of his endeavor to rebuild the Jedi Order, [Cal Kestis](/article/cal_kestis], a Jedi Knight, penetrated the Inquisitorius stronghold via the Defensive Perimeter. His goal was to retrieve a holocron previously taken by the Inquisitor Second Sister from Bogano, following a short fight between them.
The Defensive Perimeter was featured in the Star Wars Jedi: Fallen Order video game from 2019, which was created by Respawn Entertainment and published by Electronic Arts.