From Halopedia, the Halo wiki

The scutarii were a class of Warrior-Servant serving the Forerunner navy tasked with ship security. Heavily armored, the scutarii excelled in shipboard combat and tactical reconfiguration of their ship's interior spaces. The scutarii were charged with defending the navarch crewmen and their princeps commander.[1][2] Sojourner-class dreadnoughts carried a contingent of two hundred scutarii.[2]