The Fall of Rome scenario is included in the Gods & Kings expansion for Civilization V. It is a Classical attack/defense scenario where you must "Play as either Eastern Rome or Western Rome trying to fend off the barbarians, or as one of the barbarians themselves."
All of the civilizations are locked into war with each other, save Western Rome (the Romans) and Eastern Rome (the Byzantines), who are on a team together. The diplomacy screens are thus unavailable (as opposed to the 1066: Year of Viking Destiny scenario, where diplomacy screens can still be accessed, but are basically useless). There are three social policy trees - "Roman," "Persian," and "Barbarian" - each of which is only available to select civilizations. Western and Eastern Rome have the Roman policy tree, the Sassanids have the Persian policy tree, and the other five have the Barbarian policy tree.
The policies in the Roman policy branch only have negative effects, so as both Roman empires advance, they go further into decay. In addition, for each city the Western and Eastern Romans lose, they gain more Culture, causing their empires to go even further into decay, and it is impossible for either of them to sell buildings to reduce Culture, increase income, or reclaim precious money from a city that is about to be lost to enemies.
In the scenario, the purpose is to have the highest number of Victory Points when the time runs out. Victory Points can only be acquired in this scenario through control of imperial cities (cities that initially belonged to Western and Eastern Rome or the Sassanids) for Western Rome, Eastern Rome and the Sassanids, while other civilizations gain Victory Points by capturing these same imperial cities; each turn, the three empires will be rewarded with Victory Points based on how many imperial cities they control at the end of the turn. Western and Eastern Rome have an advantage in this arena, starting with an incredible number of imperial cities to begin with, but they come under attack from all directions almost immediately and do not have enough soldiers to properly defend against all the invading Barbarians and Persians. The Sassanids start smaller, but they get more Victory Points from each city, don't suffer the penalties the Romans do, and have only a few enemies in the beginning. Barbarians earn Victory Points and culture from capturing imperial cities; they get the points upon capture and it does not matter whether they choose to keep the city or raze it. The bigger a city is, the more points a Barbarian civ gains when capturing it. Barbarians also get extra happiness and free unit maintenance cost.
There are eight playable civilizations in this scenario:
- Western Rome
- Eastern Rome
- The Sassanids (scenario-specific civilization; uses Persia's colors)
- The Celts
- Leader: Boudicca
- Unique Ability: Painted Rebels (Combat bonus (+50%) when fighting against a civilization with more cities. Treats forests in friendly territory as roads. Embarked units have +1 Movement and pay 1 movement point to move from sea to land.)
- Unique Unit: Pictish Warrior
- Unique Building: Ceilidh Hall
- The Franks (scenario-specific civilization)
- The Goths (scenario-specific civilization)
- The Huns
- The Vandals (scenario-specific civilization; uses Songhai's colors)