I've always speculated that the war started shortly after the Great Schism when both civilizations had warp drive, split apart, bombed each other back into the Stone Age and then had to discover Warp again. That would also account for what we would guess are the vast differences in the Romulan and Vulcan versions of warp propulsion.

Regarding the Romulans and warp drive, this is one the first questions I ever asked on the forum a few months ago. It was covered pretty extensively in this thread: http://flare.solareclipse.net/Forum6/HTML/000202.html and http://flare.solareclipse.net/Forum6/HTML/000202-2.html

I used the answers to the questions to write my most recent article for the Starfleet Museum (http://www.uni-siegen.de/dept/fb12/ihe/bs/startrek/sfmuseum/romulan-war.htm). I figured the best answer was that both the Romulans and Earth had warp drive. At the start of the war, both sides used fusion power, but then earth developed antimatter drives, as used in Daedalus. The Romulans wasted all their time trying to harness quantum singularities but didn't succeed for a another two centuries. Since Balance of Terror says that the two sides never saw each other up close, I'm guessing the border at the start of the war isn't too much different from the current border.

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When you're in the Sol system, come visit the Starfleet Museum

Were this true, then Romulans certainly wouldn't need warp drive for "Balance of Terror" to work (except as the drive system of their plasma weapons - manned warpships might be more difficult to create than unmanned warp weapons). So could the Romulan Star Empire have lacked warp drive until the TOS era and the alliance with Klingons?

One argument against that is the existence of offshoot colonies in "Gambit". But those could have been founded by sublight ships, similar to those the Romulans would have used in a migration from Vulcan to Romulus/Remus. "Gambit" states that some of these colonies are in different sectors, but perhaps sectors in the vicinity of Romulus are very small for historical reasons (dating back to the times when ships were slow so space had to be divided into smaller volumes for organizational purposes). And the planets need not be full 20 ly away from each other to be in different sectors, even if sectors are 20x20x20ly^3.

Also, the Encyclopedia makes some veiled remarks about the ancient Romulans having "spanned the quadrant". What would be the exact "Gambit" reference used as the source? And could this simply mean "quadrant" in the sense the word is used in, say, STII (apparently 1/4 of a sector)?

If the "Gambit" references can be explained away, then I can't think of any other evidence that would require the pre-TOS Romulans to have been warp-capable. I don't even remember clear evidence that the RNZ would have to be bigger than 1 ly across overall, or house more than one system - has another Romulan star system ever been mentioned besides the Romulus/Remus/Romii one?

After all, "Balance of Terror" does define the RNZ as a zone that "separates the planets Romulus and Remus from the rest of the galaxy", as the quote goes. And in that episode, a Romulan ship zips between outposts seen on that map using an impulse drive (although there is nothing to say the ship couldn't have had a warp drive aboard, and simply would not have turned it on). Most explicitly, the ship proceeds from the last outpost it destroys to the RNZ using only impulse engines (the Enterprise tracks the ship and predicts her course by assuming an impulse drive, and since they do not lose their prey, she must be moving at impulse as assumed). If the map is even roughly to scale, then this last bit of info means that the said scale is really small, and we could be looking at a single system.

Assuming the "empire" consisting of a single system (at least after the war which they lost) lies sufficiently close to Earth or Vulcan, say, 25-50 ly, then cloaked sublight ships could easily reach Earth or Vulcan. Even uncloaked ships could have been a threat back in the 2150s when sensor ranges were short and starships few. And after TOS, an "empire" with cloaks and Klingon-borrowed warpships would be a threat indeed, regardless of whether it had one planet or one hundred.

We have seen how costly it is to attack a star system in DS9. If the Romulans have fortified theirs sufficiently by the time of TOS, they could lay waste to the nearby Earth from this invulnerable base.

At some point in their ancient history the Vulcans are technologically advanced species with warp capability but still suffer from their un-suppressed emotions. A savage war breaks out between separate factions. Those who follow the new philosophies of Surak and the those who will eventually come to be called the Romulans. After nearly a hundred years war in which off-Vulcan colonies are destroyed and much of the civiliation is bombed back into the Stone Age the Romulans take the few remaining warp-capable ships and leave for a new home. Some ships are lost along the way, others find homes for themselves (the ruins from Gambit, see also Spocks comments in Paradise Syndrom) and the outlying colonies are either cut off or destroyed leaving a decimated populus on Vulcan and a band of stragglers headed toward Romulus.

After a period of time the Vulcans recover under the leadership of T'Planahath and soon are exploring the galaxy again, unaware of what has become of those who left (Balance of Power - Spock apparenty isn't aware of the existence of the Romulans).

The Romulans, the few that are left after their journey, make a home on Romulus and begin building a civilization basically from scratch. Though they retain some techonologies they revert to more primitive things in others (not an unheard of thing - witness the Middle Ages) including the non-warp drive that their ships are equipped with at the time of the war with Earth.

NOTE: Though we know Earth and Romulus fought a war that occurred after First Contact with the Vulcans we don't know for certain what type of contact there was between them. They could have been faceless enemies, which would explain a lack of knowledge about them, who were identified only post facto. Or Earth and Vulcan ties weren't so close (or were just too new) at the time of the war so the Vulcans weren't told everything.

http://www.icok.net/~fearless/fcis/rhistory.html

The best entries are:
462 A.D- Geological prospecting reveals that there are no subspace-active materials in the Romulus system. Long range scans by probe ships show that nearby systems. The Empire begins to expand using ancient sublight colonization techniques, which will take centuries.

1542 A.D.- Romulan sublight ships find limited amounts of subspace active materials. Within 10 years a small handful of warp capable ships are built. The Empire develops a unique style of transport, large carrier ships convey up to one thousand in their hulls and even entire vessels within their warp fields. This system works safely for centuries.

and here's something else dealing with Romulan Technology, but I'm not sure if it'll help or not.
http://www-rcf.usc.edu/~j1542 A.D. ason/dummies4.htm

Whether the romulans could have set up an empire on the far edge of the Federation without FTL depends on how large the Federation is and how far Romulus is from earth. Supposedly the Federation is thousands of light years in diameter. If the romulans didn't have FTL, they could travel at a maximum of 1 light year per year. If the schism that drove them from Vulcan occurred 2000 years ago, they couldn't be more than 2000 light years away and probably much less. If the schism occurred more recently, they would have to be even closer. So, as jh says, warp drive is probably needed in the past to establish the empire. jh's suggestion that the Romulans lost warp capability after reaching their new homes is possible, but I think it's not necessary, unless you believe that the fought the E-R War without FTL.

For the record, here's what spock says about the War (I transcribed this in a hurry, but I think I got most of it): "Referring to the map on your screens, you will note beyond the moving position of our vessel a line of Earth outpost stations. Constructed on asteroids, they monitor the neutral zone, established by treaty after the Earth-Romulan conflict of over a century ago. As you may recall from your histories, this conflict was fought, by our standards today, with primitive atomic weapons and in primitive space vessels, which allowed no quarter, no captives. Nor was there even ship-to-ship visual communications. No human, Romulan, or ally has ever seen the other. Earth believes the Romulans to be warlike, cruel, treacherous. And only the Romulans know what they think of Earth. The treaty, set by subspace radio, established this neutral zone, entry into which by either side would constitute an act of war."

How wide is the neutral zone? I had always assumed that it was at least a light year wide. Maybe by judging the speed of Enterprise the scale of this map can be figured out.

Also note that in this episode, there is no mention of who won this conflict. The idea that Earth prevailed was later introduced only in the TNG era, with the establishment of the Battle of Cheron.

A strange thing about this episode is the distinction drawn between invisibility and sensor detectability. A major plot device is that while the Romulan ship cannot be seen, it can be tracked by sensors. Similarly, although the Romulans cannot see Enterprise they can detect it with sensors but dismiss is as a sensor echo. Therefore, the cloaking device as seen here is the equivalent of darkness or a thick fog. As with modern aircraft, most combat in space will probably occur without visual contact. I haven't seen "The Enterprise Incident" for about 15 years (yes, I'm about 150 years old), so I can't comment on how cloaking device is treated in that episode. However, by the TOS movies, the cloaking device prevented both visual and sensor detection.

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When you're in the Sol system, come visit the Starfleet Museum

And I think the only thing "misleading" about Scotty's line is that everyone assumes that "impulse" means the subluminous propulsion and nothing else. However, I'm pretty sure he said "impulse power". Impulse power is not the same thing as impulse drive.

Scotty: They have only impulse power, Captain.
Kirk: You mean only impulse drive?
Scotty: No, I mean warp drive powered by a fusion reactor.
Kirk: Then why didn't you say so, you drunken idiot.

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When you're in the Sol system, come visit the Starfleet Museum

However possible that scenario would be, I still prefer to interpret things so that Romulans always had interstellar warp and used that tech to move from Vulcan to Romulus. It's just that not all of their warships possess that drive. There is little need for it if the Romulans are not allowed out of their home system, after all. The ship seen in "BoT" could have been a warp-driven patrol vessel similar to those seen intercepting the Enterprise in "The Deadly Years", simply modified so that the drive is replaced by the cloaking device (or power rerouted so that the cloak uses it all up).

Here's the first on there History: http://www.icok.net/~fearless/fcis/rhistory.html

And some sites about them/and or, on their Technology: http://www-rcf.usc.edu/~jason/index.html http://sac.uky.edu/~jmosbo0/Mem_A/romulan.html http://pages.prodigy.com/nadel/aliens.htm http://www.startrekker.net/peoples/romulan.shtml http://startrek.about.com/entertainment/startrek/msub19.htm?once=true&

So far, this was all I could find, hope they help!

For reference, here's what spock says about the Romulans in "Balance of Terror:"

Spock: And if the Romulans are an offshoot of my Vulcan blood -- and I think this likely -- then attack becomes even more imperative.
McCoy: War is never imperative, Mr. Spock.
Spock: It is for them, Doctor. Vulcan, like earth, had its aggressive, colonizing period. And if the Romulans retain this martial philosophy, then weakness is something we dare not show.
McCoy: Do you want a galactic war on your conscience?

Does this passage suggest that Humans were aggressive colonizers sometime between the 2260s and the start of the FTL age in the 2060s? Was Earth possibly the aggressor in the war? Or is Spock just pointing out savage events that occurred on Earth itself, before the space age, as he likes to do?

Here's the part where they talk about the Romulan ship:
Kirk: Well, gentlemen, the question still remains: can we engage them with a reasonable possibility of victory?
Scott: No question. Their power is simple impulse.
Kirk: Meaning we can outrun them.

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When you're in the Sol system, come visit the Starfleet Museum

In fact, if the Romulans only had impulse drive, Kirk would be making the understatement of the twenty-third century by saying the E could outrun them. I think Kirk was well aware that Scotty meant that the Romulans' warp drive was powered by the same fusion reactions that are the basis of "impulse", and that this placed their top warp speed much lower than the E's.