Rome, also known as The Roman Empire, is economically and militarily the strongest country in the first centuries of the timeline. It is playable at all start dates between 2 and 395. The Roman Empire is located in Western and Eastern Europe, North Africa and part of the Middle East. The country borders its rival, 
Parthia, in the east, minor African tribes at the south, and mostly barbaric German tribes in the north.
The Romans at the 2 A.D. start begin with 8 vassals: 
Mauretania, 
Odrysia, 
Cappadocia, 
Pontus, 
Bosporus, 
Iberia, 
Judea, and 
Corduene.
Despite being the most powerful nation in the world at that time, they aren't by any means invincible. If the player isn't careful enough, the Roman Empire will fall. To ensure that an empire of that size doesn't fall due to religious intolerance or nationalism. In the first two centuries, Celtiberian and Gallic from the Celtic culture group are accepted, as well as Greek, Illyrian and Roman from the Byzantine culture group are accepted cultures at the start.
See also: 
Byzantium, 
West Rome, 
Gallia, 
Egypt, Parthia, 
Pictland, 
Dacia, 
Huns, 
Sassanid, 
Italy, 
Soissons
Strategy
Startdate
It's strongly advisable to play the The Roman Empire at the year 116, at its height according to the mod. Despite all the debuffs Rome gets, Rome is still very powerful militarily (number one in fact) and the largest nation at that time, with nothing serious to worry about. The only exception to this is Rome's one weakness: 
stability. Whatever you do, never get negative stability or else...
Roman-Parthian War
The Roman Empire is considered an interesting choice during this period. The player should be careful for the Parthian military force which is powerful due to its 
cavalry.
Religion
Ignore the rise of Christianity. Focus your missionaries on the various pagan religions to 
Hellenism until mid-late 300's AD. This will maintain your religious unity and pave the way for the rise of Christianity. Once 
Chalcedonian begins to spread on its own at a quicker pace, you might want to consider converting and spreading the new faith over Hellenic territory as quickly as possible as your territories will be unhappy with the change. Convert to Chalcedonian when you have plenty of 
administration points, max stability, and happiness in the realm.
Culture
Spread Roman culture as close to Italy as possible with the intent of solidifying the Roman borders around Italy in case the 
Barbarian horde broke through the provinces. It can also be used as a tool to eliminate nationalism in North Africa as the cost of conversion is low. It might even be beneficial to assimilate Britain once the 
Druidist religion is eliminated as another fall back safeguard. Beware of changing the culture of Egypt, anywhere in the Middle East, and Northern France. It's usually the case that Gallic rebellions can eliminate all the progress you've made in France, and others elsewhere. Also, avoid changing Greek, Illyrian and other accepted cultures, because this will only waste your 
diplomatic points.
Barbarian Invasion
At a certain point in the game, after 395, the Germanic Tribes as well as Pictland and Irish Tribes will declare war on you in mass even if you have an alliance with them. If you defeat them, they will re-declare war shorty after the truce expires. They will receive immense bonuses to military power and will most likely be unstoppable and lead to the historic downfall of the Roman Empire.
The Barbaric Wall
A good strategy to prevent the barbarian sack of Rome is to create Germanic 
vassal states early in the game covering all of your German borders (from the North Sea to the Black Sea). Sell captured territory or Roman territory itself to your vassals so that the unvassalized horde has no border with Rome, and they will not attack your German puppets.
Annexation
Alternatively, focus attention on Germanic tribes exclusively and annex/vassalize all of them before 395. Even if Pictland and Irish Tribes remain unconquered, they pose little risk to the Empire due to their lack of naval dominance and transportation.
Country Conversion
Another possible strategy is to initiate a cultural shift as to form an entirely new country, as the barbarian tribes can only invade Rome, Western Rome or the Byzantine Empire. After the Barbarian Invasion, it should be fairly easy to claim both the Mashriq Region and the British Isles necessary to restore the Empire afterward.
Three more or less easy-to-form country are possible, with some others that are more difficult even : these three are the country of Egypt, 
Spain (after adm tech 10) and 
France.
Since Rome possesses most of the kemetic egyptian provinces, it is fairly easy to initate a cultural shift after displacing some states and forming kemetic Egypt.
France and Spain are a little more difficult to form, as it is necessary to switch to Basque culture beforehand; if you haven't annexed 
Vasconia, you possess only one Basque province. However, being able to switch to Basque to form France or Spain give you the incredible bonuses their starting ideas provides, in the case of Spain, and in the case of France, their extremely powerful morale boost after the third idea group completed, both of which will be coupled with the Roman Empire government type, already adding 10% land morale bonus.
Other formable nations for Rome include:
Israel (necessitate a religious shift to Judaism)- Assyria or Babylon if Rome controls the Mashriq and switches to either assyrian or babylonian culture
Rebels and Unrest
Avoid 
over-extension at all costs - you've got time, expand slowly. Increase 
autonomy whenever necessary. A lower income is favorable to rebels.
Mercenaries
The relatively 
low manpower but strong economy of the Roman Empire suggest the use of 
mercenaries. Replace all standard infantry with mercenaries, therefore preserving your manpower. Use normal cavalry for cost-saving. The manpower will only be used to replace cavalry losses; the costs are usually manageable.
Decisions
Reform Hellenism (before 380)
Requirements:
- Administrative Tech at least 9
- Administrative Power at least 50
- Own at least 20 provinces in the Christian religious group.
Upon Enactment:
- Lose 50 Administrative Power
- Gain country modifier Reformed Clergy until the end of the game.
- +10% Stability Cost Modifier
- +1% Missionary Strength
- +1 Tolerance of the True Faith
- -2 Tolerance of Heathens
- +10%
End Pax Romana
Requirements:
- Has modifier Pax Romana
- Does not have modifier Empire Collapsing
Upon enactment:
- Removes Pax Romana modifier
- Lose 2 Stability
- If does not have modifiers: Empire Destabilized, Empire Declining, Empire Fragmenting, Empire Collapsing, or Total Collapse.
- Receive Empire Destabilized modifier
- If have Empire Destabilized modifier, then receive Empire Declining modifier
- If have Empire Declining modifier, then receive Empire Fragmenting modifier
- If have Empire Fragmenting modifier, then receive Empire Collapsing modifier
- If have Empire Collapsing modifier, then receive Total Collapse modifier
Declare Pax Romana
Requirements:
- Has Stability at Least 1
- Is at Peace
- Number of Revolts is less than 1
- War Exhaustion is less than 2
- Does not have modifier:
- Pax Romana
- Total Collapse
Upon enactment:
- Adds Pax Romana modifier
- Adds Country Restabilized modifier for 5 Years
- If have Empire Destabilized modifier, Remove Empire Destabilized modifier
- If have Empire Declining modifier, Remove Empire Declining modifier, Receives Empire Destabilized modifier
- If have Empire Fragmenting modifier, Remove Empire Fragmenting modifier, Receives Empire Declining modifier
- If have Empire Collapsing modifier, Remove Empire Collapsing modifier, Receives Empire Fragmenting modifier
Technology Reform
Requirements:
- Have Roman technology group.
- Is at Peace
- Has Stability at Least 2
- Administrative technology at least 46
- 100 Administrative power
Upon Enactment:
- Lose 100 Administrative Power
- Lose 2 Stability
- Technology group is changed to "Eastern"
- Unit types are changed to "Eastern"
Government Reform
Requirements:
- Has the government "Roman Empire" (government at start)
- Is at peace
- Has Stability at least 1
- Administrative technology at least 12
- 200 Administrative power
- Imperial faction is in power
Upon Enactment:
- Lose 200 Administrative Power
- Lose 1 Stability
- Government type is changed to "Despotic Monarchy"
Division of Rome
Requirements:
- Owns: Roma, Constantinople
- At peace
Upon Enactment:
- Gain 1 Stability
- Gain 50 Administrative Power
- Gain 50 Diplomatic Power
- Gain 50 Military Power
- Rome splits into:
Mend The Great Schism
Requirements:
- Is Orthodox
- Is at peace
- Is not a subject nation
- Country is:
- Owns Orthodox Province: Roma, Constantinople, Syracuse, Beroea, Judaea, Alexandria
Upon Enactment:
- Gain 25 Prestige
- Gains Schism Mender Flag
Ban Christianity
The AI will never pass this decision.
Requirements:
- Is either Rome, West Rome or Byzantium
- Is Hellenic
- Has any Chalcedonian province
- Administrative Power at least 50
Upon enactment:
- Lose 50 Administrative Power
- Gain "Christianity banned" until decision Legalize Christianity is taken:
- +2% Missionary Strength
- +1 National Unrest
- -2 Tolerance of Heathens
Legalize Christianity
AI will always pass this decisions
Requirements:
- Has banned Christianity
- Administrative Power at least 50
Upon enactment:
- Lose 50 Administrative Power
- Lose country modifier "Christianity banned"
Restore the Roman Empire
Requirements:
- Is in the Christian or Hellenistic (Greco-Roman) religious group
- Is not:
- Rome does not exist
- Is not a nomad nation
- Is not a subject nation
- At Peace
- Owns the following regions: Italy, France, Iberia, Balkans, Anatolia, Mashriq
- Owns Core Provinces: Fez, Tunis, Cairo, London, Yorkshire, Zeeland, Vienna
Upon Enactment:
- Country changes to Rome
- Primary culture changes to Roman
- Culture of all provinces of former primary culture is changed to Roman
- Trigger country event "New Traditions & Ambitions"
- Capital moves to Rome
- Gain core on Rome
- Set government rank to Empire
- All owned provinces are removed from the Holy Roman Empire.
- Gain 50 Prestige.
- Gain country modifier Increased Centralization for 20 years:
- -0.05 Monthly Autonomy Change
- +1 National Unrest
- -0.05
Roman Ideas and Traditions
Traditions:
- +10% Infantry Combat Ability
Ideas:
- Flexible Recruiting: +20% Manpower Recovery Speed
- Skilled Commanders: +1 Land Leader Maneuver
- Scorch the Lands and Poison the Wells: +1 Attrition for Enemies
- Latin Islands: +1 Yearly Legitimacy
- Peasant Soldiers: +10% National Manpower Modifier & -10% Infantry Cost
- Phanariote Traders: +15% Global Trade Power
- Phanariote Taxes: +10% National Tax Modifier
Ambitions:
- -20% Land Maintenance Modifier