The Romulan Star Navy was the primary space forces of the Romulan Guard, the military force of the Romulan Star Empire. Also known as the Grand Fleet or Imperial Fleet ("galae" in the Rihannsu tongue).
The Romulan Star Navy uses a complex organisational structure for its spaces forces. Its fleets are based around particular groups, such as Command Fleets, Praetorian Fleets, Senatorial fleets, Coalition fleets and others. These fleets are then usually assigned to specific "commands", such as Star Command, Exploration Command, Pacification Command or Occupation Command. These fleets are made up of several avaras or 'centuries' of around a hundred vessels. Avaras are then broken down into command wings of ten to twenty vessels, named after the lead vessel (called a 'wingship') of the wing. (The Dominion War Sourcebook: The Fires of Armageddon)
During the Dominion War the Romulan Star Navy contributed around 7,000 vessels split into twenty-five fleets. Fourteen of the fleets were command fleets with the rest mainly senatorial or coalition fleets from factions that supported the declaration of war against the Dominion. Sufficient forces were left in the empire to guard against other threats. (The Dominion War Sourcebook: The Fires of Armageddon)
In Remington continuity, Starfleet and the Star Navy had established an officer exchange program in light of the newly-peaceful relations between the two navies' governments. However, the peace was shaken by the defection of a significant portion of the Star Navy to the Romulan Confederacy. The defectors, along with those who defected from the Tal Shiar, formed the Confederate Fleet.