Religion
Medieval Total War
Rome: Total War: Barbarian Invasion
In Rome: Total War, all factions all can build monuments to their gods which only affect the happiness of a settlement. However, in the Barbarian Invasion expansion religion has been reworked entirely.
Religion has become extremely important in people's lives. In the early days of the Empire, religions could quite easily co-exist peacefully but times have changed and religious unrest is now very common.
Religion affects a settlement's happiness considerably. Building a Christian church in a mainly Pagan province will result in considerable unrest and possibly even rebellion. Placing a Pagan temple in a Christian town can cause the same problems. In order to appease their subjects, factions can also decide to build religious buildings of the same religion which is prevalent in a region - even if the faction's main religion is a different one.