The Romulan Star Empire (or simply the Romulan Empire) was a major interstellar state encompassing the Romulan people and their subject worlds and species. The Empire was known for its xenophobic character and policies of extreme secrecy, subterfuge, and territorial expansionism. By the late 23rd century, the Empire counted among the great powers in its region of the Milky Way Galaxy until the destruction of Romulus and its replacement by the Romulan Free State.
- Main article: Romulan history
The Romulans originated from dissident Vulcans who rejected Surak's philosophy of peace, during the Time of Awakening and emigrated from their homeworld around the 4th century. They settled on the planets Romulus and Remus, subjugating the native Remans in the process. (TNG: "Gambit, Part I"; Star Trek Nemesis) The development of warp drive enabled the Romulans to expand their state into a Star Empire. (Star Trek: Insurrection)
In 2152, the Romulans came into contact with the Human starship Enterprise. (ENT: "Minefield") Relations between the Empire and United Earth deteriorated as the Enterprise crew thwarted a Romulan plot to subvert the Vulcan High Command. (ENT: "Kir'Shara") Recognizing the growing threat posed by Earth, the Romulans attempted to incite war in the region by attacking civilian shipping using disguised drones. The effort, however, backfired, as their involvement was exposed by Enterprise and spurred the formation of an alliance between the Humans, Vulcans, Andorians, and Tellarites, the nucleus of what would become the United Federation of Planets. (ENT: "Babel One", "United", "The Aenar")
Open war erupted between Earth and the Romulans in 2156, ending four years later with a humiliating Romulan defeat at the Battle of Cheron. An ensuing peace treaty established the Romulan Neutral Zone, after which the Romulans had no substantial contact with Humans for a century. In 2266, the Romulans tested Federation resolve by sending a Bird-of-Prey to attack Federation outposts along the Neutral Zone. The defeat of the Bird-of-Prey by the USS Enterprise averted war. (TOS: "Balance of Terror"; TNG: "The Defector") During this period, the Romulans experienced a short-lived break in their enmity with the Klingons, resulting in a technological exchange between the two. (TOS: "The Enterprise Incident")
The Romulans viewed the 2293 Khitomer Accords between the Federation and the Klingon Empire unfavorably, as it shifted the balance of power against them. (Star Trek VI: The Undiscovered Country) Escalating hostilities between the Star Empire and the Federation culminated in the Tomed Incident of 2311 and the Treaty of Algeron. The Romulans again ceased meaningful contact with the Federation, though they continued to war intermittently with the Klingons. In 2364, the Empire began to engage once more with the Federation, following a series of mysterious attacks on their Neutral Zone outposts. (TNG: "The Neutral Zone", "The Defector", "Yesterday's Enterprise", "The Pegasus") The Star Empire also launched at least one attempt to infiltrate the Federation, creating a clone of Starfleet Captain Jean-Luc Picard of the USS Stargazer who came to be known as Shinzon. This plot was abandoned after a shift in power in the government, leading to Shinzon being condemned to the dilithium mines of Remus. (Star Trek Nemesis)
For the latter part of the 2360s, the Romulan Star Empire was locked in a cold war with the Federation, launching repeated probes of Federation space and subversive actions. Most significantly, they attempted to break the Federation-Klingon alliance, resulting in the Klingon Civil War, and to exploit the Vulcan reunification movement to invade Vulcan. Both plans were unsuccessful. (TNG: "The Enemy", "Redemption", "Redemption II", "Unification I", "Unification II") At some point after resuming contact with the Federation and learning of the existence of Soong-type androids such as Data and Lore, a Romulan Zhat Vash agent began infiltrating Starfleet under the alias Oh. (PIC: "Broken Pieces")
The Star Empire's position shifted when violent contact with the Dominion in 2370 presented a common threat to all Alpha Quadrant powers. The Romulans collaborated with Starfleet in a limited fashion to counter the Dominion threat by allowing the installation of a cloaking device aboard the USS Defiant. (DS9: "The Search, Part I") By late 2373, however, they opted to sign a nonaggression pact with the Dominion. (DS9: "Call to Arms")
In mid-2374, the Romulan Star Empire was brought into the Dominion War on the Allied side through an act of subterfuge by Starfleet Captain Benjamin Sisko and former Obsidian Order agent Elim Garak. (DS9: "In the Pale Moonlight") Romulan participation marked a turning point in the war and was critical to the defeat of the Dominion, the following year. (DS9: "Tears of the Prophets", "What You Leave Behind")
During the war, Shinzon was among those conscripted from the mines of Remus to serve as shocktroops. He distinguished himself in battle, and became a respected leader among the Remans; he and his followers began amassing greater power within the Empire. In 2379, Shinzon seized control of the government, assassinating the Senate and declaring himself Praetor. He subsequently attempted to launch a genocidal attack on Earth, only to be stopped by the USS Enterprise-E, the Romulan warbird Valdore, and one other Valdore-type warbird. It was hoped, by members of both sides, that a lasting peace between the Romulans and the Federation would follow. (Star Trek Nemesis)
In 2387, the Star Empire suffered a terrible blow when the supernova of the Romulan sun destroyed Romulus. (Star Trek) By 2399, it had been supplanted or at least partially replaced by the Romulan Free State. At least one of its key agencies, the Tal Shiar remained in existence, transferring its loyalties to the Free State. (PIC: "Maps and Legends")
- See: Romulan space
The ruling body of the Romulan Star Empire was the Romulan Senate, with each senator representing a province. The Senate was led by the Praetor, followed by the Proconsul and then the Vice-proconsul. The Praetor also presided over the Continuing Committee, a powerful body that held authority over Senate members. Changes of government and attendant shifts in policy were not uncommon in the Empire. (TNG: "Unification I"; DS9: "Inter Arma Enim Silent Leges"; Star Trek Nemesis) In 2373, Q stated that, at one point, he could have produced offspring with the Romulan empress if he wished to do so. (VOY: "The Q and the Grey")
The Romulan Senate dispatched ambassadors from time to time, for example Caithlin Dar to Nimbus III and Nanclus to the United Federation of Planets. (Star Trek V: The Final Frontier; Star Trek VI: The Undiscovered Country)
In external application, Romulan political agendas appeared largely unified over the centuries. Their goals focused on maintaining Imperial security through vigilance, and negating the perceived advantages of their rivals. Both goals were accompanied by a near-paranoid reticence to reveal information, even facts as basic as their racial identity, that might illuminate other Romulan ambitions or motivations. Short of war, the means to those ends have generally varied between favored methods:
- Surreptitious political disruption of rivals – as in the secret relationship with V'Las of the Vulcan High Command in the 2150s, participation in the Khitomer conspiracy of 2293, secret alliances both with the Klingons, such as in the House of Duras from the 2340s, or against the Klingons, or the aborted attempt to replace key Starfleet officers with clones in the late 24th century. (ENT: "Kir'Shara"; Star Trek VI: The Undiscovered Country; TNG: "Sins of the Father", "The Mind's Eye"; Star Trek Nemesis)
- Limited, surprise or covert military action – as in the use of telepresence-operated drone ships to spark the "Babel Crisis" among neighboring powers in 2154, a single Bird-of-Prey used to attack the Federation border and gauge its weaknesses in the Neutral Zone Incursion of 2266, or the attack on the Klingon outpost at Narendra III in 2344. (ENT: "Babel One", "United"; TOS: "Balance of Terror"; TNG: "Yesterday's Enterprise")
The Empire did resort to open warfare when it was deemed necessary, but in typical fashion, their reasons for war were less than candidly expressed, as in the Earth-Romulan War and the enigmatic Tomed Incident of 2311. Unlike the Klingon objectives of the Federation-Klingon War of 2267, Romulans do not appear to have gone to war with neighboring powers under a flag of "expansion", and no competition existed for the development of class M worlds along the Romulan Neutral Zone. Romulans expressed little resentment for the negotiated Zone they zealously guarded, and following their conflicts, the Empire withdrew behind the safety of the buffer for many decades of self-imposed isolation from Federation affairs. (TOS: "Balance of Terror", "Errand of Mercy", "The Trouble with Tribbles"; TNG: "The Neutral Zone")
Subsequent to Shinzon's coup, some Romulan officers suggested that an era of warmer relations may be beginning with the Federation after Starfleet and Romulan military personnel cooperated to defeat Shinzon's forces before he could destroy Earth itself. (Star Trek Nemesis) However, during the years leading up to the destruction of Romulus, there was profound skepticism in the Romulan government about the idea of accepting Federation assistance in evacuating the Homeworlds. Picard himself, having been promoted to admiral and assigned to coordinate the Federation rescue fleet, had to testify to the reconstituted Senate in the Hall of State to persuade them to accept Federation assistance – creating a bitter sense of betrayal when the Federation withdrew its offer of help subsequent to the Attack on Mars. (PIC: "Absolute Candor")
- Main article: Romulan military
- See also: Romulan Guard, Romulan uniform, Romulan ranks, Romulan starships
The Romulan military was a powerful and technologically advanced force encompassing both spacefaring and ground forces. (TNG: "Unification II") Despite being defeated by Earth in the Earth-Romulan War of the 2150s, the Romulan Star Empire continued to be a powerful presence, not afraid to tempt Starfleet by entering the Neutral Zone. Romulan forces were a deciding factor in the Dominion War, whose entry in 2374 turned the tide of war in favor of the Allies. (TOS: "Balance of Terror"; DS9: "In the Pale Moonlight")
Besides regular forces, the Romulan Tal Shiar and Zhat Vash also had its own fleet of starships, and were a ruthless and powerful organization within the Empire and beyond. (TNG: "Face of the Enemy"; DS9: "The Die is Cast"; PIC: "Et in Arcadia Ego, Part 2")
Science and technology
- Main article: Romulan technology
The double-headed bird of prey emblem of the Romulan Star Empire was first introduced in "The Neutral Zone". The symbol was designed by Monte Thrasher. (The Official Star Trek: The Next Generation Magazine issue 12, p. 54) A Romulan emblem was seen in "The Enterprise Incident", though it was never used again. 
Paul Schneider, writer of "Balance of Terror", based many of the elements of the Romulan Star Empire such as Praetor, Proconsul, and the Romulan Senate on the Roman Empire. See Romulan - Background information for more information.
In dialogue, the Romulan Star Empire has been exclusively referred to as an Alpha Quadrant power. It has also been stated that the space of the Romulan Empire was surrounded by the territories of the Cardassians, Klingons and the Federation.
The first time this fact began to be established occurred in Star Trek: Deep Space Nine, in the episode "The Search, Part II", where the Romulan Star Empire was identified as one of the great powers of the Alpha Quadrant. For the Dominion, there were four great powers in this quadrant: the Federation, the Klingons, the Romulans, and the Cardassians. With the Battle of the Omarion Nebula, two of these threats had been reduced in effectiveness – the Romulans and the Cardassians. By "Call to Arms", the Cardassians were in an alliance with the Dominion and three powers, small and great, had signed non-aggression pacts with the Dominion. These powers were the Miradorns, the Tholians, and the Romulans. In the opinion of Odo, the Dominion was "making impressive inroads into the Alpha Quadrant."
In "In the Pale Moonlight", it was revealed that the Dominion forces were crossing the Cardassian-Romulan border and were launching attacks against Federation ships from there. When Benjamin Sisko was attempting to persuade Senator Vreenak to consider having the Romulans join the offensive against the Dominion, Sisko said, "I'd pick the side most likely to leave us in peace when the dust settles. Maybe you're right. Maybe the Dominion will win in the end. Then the Founders will control what we now call Cardassia, the Klingon Empire and the Federation. So, instead of facing three separate opponents with three separate agendas, you'll find yourselves facing the same opponent on every side. There's a word for that. Surrounded."
The association of Romulus with the Alpha Quadrant was carried over to Star Trek: Voyager. In "Flashback", Captain Kathryn Janeway reminisced about what it would be like to live in James T. Kirk's era, with "the Alpha Quadrant still largely unexplored," and "Romulans hiding behind every nebula." In "Message in a Bottle", a section of the Romulan border was identified to be located near the edges of the Alpha Quadrant. In "Bliss", when it seemed that the USS Voyager would find a way back home, Tom Paris stated that he looked forward to encountering Cardassians, Ferengi, and Romulans again in the Alpha Quadrant. In "Flesh and Blood", Chakotay identified the Romulan disruptor as an Alpha Quadrant weapon. In "Q2", in a simulation, several Alpha Quadrant species were fighting over mining rights to a planetoid, and Q Junior had to find a way to settle the dispute. The species listed were the Nausicaans, the Bolians, the Cardassians, the Romulans, the Ferengi, and the Bajorans.
In virtually all reference works, however, the Romulan Star Empire has been depicted to be located in the Beta Quadrant, with a border only with the Federation and the Klingon Empire. These books include such works as the Star Trek Encyclopedia (3rd ed., p. 43, 393), Star Trek: Deep Space Nine Technical Manual (p. 2), Star Trek: The Next Generation Technical Journal (p. 9), Star Trek: The Next Generation Writers' Technical Manual (p. 20), Star Trek: Voyager Technical Manual (p. 27) and Star Trek: Star Charts (pp. 45, 55, 56, et al.). Even reference works that date back to a time before the Alpha and Beta Quadrant distinction was invented show the Romulans in the area that was later classified as the Beta Quadrant. These include such works as the Star Trek Star Fleet Technical Manual (T0:02:07:00) and Star Trek Maps (Chart A). Only one of these graphics was reused on-screen, as a display graphic on a PADD in Star Trek: Insurrection.   The information on the PADD, though, was completely illegible on screen. 
In the video game Star Trek: Encounters, the Romulans mostly play the villain role in the levels based on Star Trek: The Next Generation. However, in the game's last level, a temporal anomaly near Earth causes the USS Defiant to briefly appear in an alternate timeline where the Romulan Empire has conquered the Federation.
In Star Trek Online, the Empire is in a state of inner turmoil after the destruction of their homeworld due to a supernova. They are now led by Empress Sela and blame the Federation for the destruction of their home planet, an event that led to a renewal of hostilities between the Romulan Empire and the Federation. Members of the Reman resistance and the Vulcan reunification movement have also established a Romulan Republic on "New Romulus" as a democratic state, allied with the Federation and the Klingon Empire in opposition to Sela's dictatorial regime. The new Romulan Republic play a major role in STO's first expansion, Legacy of Romulus.