ROME
The Glory of Rome +25% production to any building already built in the capital.
Legion - Replaces swordsman, increased combat score and production cost.
Ballista - Replaces catapult, increased ranged combat score.
Start Bias - None
The Roman civilization has two unique units, both encouraging city attacking, and both in the same era as well. The leader trait, The Glory of Rome, increases production for any building already built in the capital by 25%. In Civ4, this ability would have been ridiculous, but Civ5 has a production problem. Normally, building maintenance and long production times for buildings will lead to city specialization: only trade post cities build markets, only production cities build barracks, etc. This would result in a rather weak trait if you don't accommodate for it. Make sure you capital is a production city - save forests to build lumber mills, for example, and try to build every building available in the capital. It would be helpful if your capital has iron or marble to enhance its production, but you can't accommodate for luck like that. You will be paying a bit more in maintenance, and not building as many wonders or units as you normally would in a production city, but the long term benefits for a large empire would overshadow these penalties.
The Legion costs 10 more production to build, and have 2 more combat power over the swordsman. This unit works very well with the Ballista, and a classical era war to expand the empire has great synergy with the leader trait. This makes playing Rome somewhat luck based, as your exceptional units are limited by iron resources. Having few or even no iron weakens the great power of the Roman Empire.
The Ballista has four more ranged combat score, and comes in the same era as the Legion, both excellent city attack units. It only has two less ranged combat than the Trebuchet, but costs much less production. It can be more cost effective to build Ballista even into the medieval era, and not upgrade the ones you have leftover from the classical era. The unfortunate problem with both unique units, is that they both require iron resource, making it hard to fully capitalize on both units in the same game.
This is how I view the romans.
Remember that the
+25% production bonus is received by all cities BUT the capital, and that it only works for buildings already up in the capital.
To best (ab)use this bonus [DEPLOY THE LATEST RESEARCHED BUILDINGS IN A FEW TURNS AFTER UNLOCKING THEM EMPIRE WIDE] [think +11 universities in under 6 turns from researching them [beware of maintenance spikes]; think +11 banks[will not add much on a mostly production based empire but it will still be significant] within 10 turns after researching them; +11 walls in 1 turn and +11 castles 2 turns latter +11 Arsenals 4 turns after that [+33 happiness in 7 turns] - PROFESSIONAL ARMY(HONOR)] you need to :
a. Have many production cities - [most of them] - look for hills and forests before settling. Improve the production tiles. Build the production relevant buildings on most cities[will add maintenance costs ...] ...[
unless the 25% percentage bonus applies to a big production base it will not add much to be significant]
b. No matter how much you pimp Rome's productivity :
-you either start production of the new critical buildings on the same time empire wide and chances are some will built it ahead of Rome [better position, railroad bonus,..] and the others will just use the bonus for a few meager turns. wasted bonus.
-you delay starting the production of the critical building on the empire until Rome finishes it. Now you are using the 25% production bonus BUT you delayed the deployment of the critical building empire wide for a significant period of time.
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you purchase the newly developed critical building on the turn its unlocked in Rome so the rest of the empire can start deployment using the full power of the 25% bonus from the same turn.
c. You will run into maintenance problems having all those production buildings. Dropping advanced buildings *X number of cities empire wide will generate serious maintenance spikes. You will need a few gold focused cities to keep up with the maintenance problems. Rome with some luck can be turned into a gold focused city to take advantage of unlocking commerce.
+
The high production capabilities can/should generate solid military.
Production focus should generate a few Great Engineers to net you a few world wonders.
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Culture will suffer - you might not afford the maintenance for the advanced culture buildings.
Budget and number of policies available will suffer - you will not be able to maintain many CS allies..
Favors domination victory. Science victory also possible because of the quick deployment of the science buildings and many production powerhouses to build the spaceship parts.
About the Legion - the ability to build roads might come handy.
-freeing the workers to improve productivity tiles
-building roads will remove the movement penalty for rough terrain [forest,hill] for your land armies[mobility around the battlefield is a great tactical advantage] while preserving the combat bonuses[again without having to displace a worker to do it].
Same for the build fort ability - build forts on borders[useless desert tiles] during peace time - workers will replace them latter if the land is valuable ..