The Theta Gate was an interdimensional teleportation device used by Blackout to bring his infinite army into the Matoran Universe. It is unknown whether Blackout found the Gate or built it. Later, Blackout reactivated the Theta Gate in response to Ynot's impending attack on Darkmount. He used it again to summon troops to attack invaders from the Shattered Mirror Universe. Seriously. Only Zev could screw up that badly.