The Narvasam class or Nestar class were a type of outpost used by the Romulan Star Empire.
This type of defensive outpost was one of the mainstays of the Imperial Navy's Outpost Division which were deployed in sensitive areas such as the Federation Neutral Zone and the Klingon border. The Nestar class stations were powered by matter/antimatter generators that were backed up by auxiliary generators that operated on principles similar to that of an impulse engine. Similar such reactors were found on Starfleet space stations which were used for energy generation rather then moving the station.
Typically, the crew of these outposts were charged with monitoring several posts along with automated sensor's on a perimeter. This led to the Romulan empire finest electronic surveilance, security and intelligence assets being found at such stations. The Commander's of these far off sentry towers were of a special breed in that they were frequently called to make life or death decisions on a split second notice. Furthermore, the station's were augmented with several smaller starships assigned under its overall command. (FASA RPG module: The Romulan Way: Game Operations Manual)