The Miridian system was a star system within Romulan space, inhabited by a race called Miridians. The system was taken by the Romulan Star Empire circa 2365, and its inhabitants made to perform slave labor.
Following the coup by Shinzon of Remus and the collapse of the Romulan government, the Miridians rebelled against Romulan rule. The Miridian system then became a stop for an "underground railroad" transporting Remans out of Romulan space.
Outpost 22 was the closest Federation installation to the Miridian system. (ST novel: Articles of the Federation)