[h1=blue]Dona Eis Religions[/h1][i]Dost thou know the magnitude of thy sin before the gods?[/i]
There are seven techs which each introduce a religion into the game. Each religion is introduced in a single city, but can spread throughout the world. Converting to a religion can provide bonus happy, more buildings to construct, diplomatic bonus (and penalties), and unlock powerful civics.
The actual mechanics of the religion engine are not always clear, so questions are common, albeit less common than wrong answers. Hence, this effort to put all of the right answers in one place.
[h2]Founding a Religion[/h2]
[b]For games that begin in the Ancient Era[/b], no civs begin the game with knowledge of any of the religious technologies. Therefore, each religion is first introduced to the game when the corresponding technology is discovered:
[b]Organized Religion[/b] Judaism
[b]Code of Laws[/b] Confucianism
[b]Divine Right[/b] Islam
[indent]In Beyond the Sword [i]Choose Religions[/i] is a custom game option that removes the relationship between a technology and the religion specific to it. If you are the first to discover a religious technology, you may choose which religion you found (save only that you may not duplicate an existing religion). Some of the AI Leaders have a preferred religion as well (defined in CIV4LeaderHeadInfo.xml), and will select accordingly. Those leaders who do not have a preferred religion defined will default to the religion normally associated with the technology.[/indent]
These religions are almost interchangeable – the strategic resource which accelerates the construction of a Cathedral is the only difference in the game mechanics.
Note that there is are no tie breaker mechanics, because [i]there are no ties[/i]. The religion is founded when you discover it (mid turn if you lightbulb the technology, between End Turn and the start of the next player’s turn if you research the technology the old fashioned way).
[b]For games which start in later eras[/b], all of the players in the game share knowledge of one or more religious technologies. These religions are distributed randomly at the beginning of turn 6 (defined in CvGame::doHolyCity). The selection process is biased in favor of human players, and in favor of spreading the religions out. Each of the religions is checked in the order listed in Civ4ReligionInfo.xml – so in single player play the human almost always founds Judaism.
[indent]In Beyond the Sword, the bias in favor of the human player has been removed. Also, the turn clock is disabled if you are playing an [i]Advanced Start[/i] custom game. Furthermore, your leader’s preference takes precedence over your own, when the religions are being dealt out.[/indent]
[h2]The Holy City[/h2]
Each religion in the game has a single Holy City, which has a special, unique relationship with that religion. In game terms, the holy city for a religion is permanent – raze the holy city, and it is not replaced; expect severe diplomatic penalties.
The holy city is important in a number of respects – it generates more culture than a converted city, it is the source from which the religion magically spreads (see below), and it is the only city in which the Shrine for that religion can be built.
The last of these is an important element of religion based strategies, as a consequence, the mystery of which city will be the source of the religion is an important one.
One important point, often missed by those who prefer single player games, is that religious technologies, like every other technology in the game, is discovered by teams, not players. In other words, when “you” discover a technology, you may find that one of your Permanent Ally’s cities is chosen has the holy seat. Which player lands the religion is determined by a random number added to the total number of religions in that player’s cities, and a 10x multiplier that biases the result in favor of those members of the team who were actively researching the tech at the time.
Once the player has been determined, that player’s cities are each checked in turn. A random seed is added to the city’s population, which then has two negative factors applied to it – an 8x bias against the city with the Palace, and a smaller bias scaled with the number of religions already present in the city.
So while you cannot assign the holy city as you might wish, you can arrange circumstances so that the biases work in your favor (keep the population high, keep the population in other candidates low, refrain from spreading religions to your preferred city, aggressively convert the other cities).
[h2]Spreading the Word[/h2]
After a religion has been founded, there are too vectors by which it may spread to another city.
At the end of each player’s turn, each of his cities is checked against each religion to see if the city will spontaneously convert to that religion. To be eligible, the city must be free of religions, and must be [i]Trade Network Connected[/i] to the holy city.
[indent]Very rarely, you will see the announcement that you have founded a religion, and immediately find that it has spread to other cities. This demonstrates the timing of the game mechanics; after you hit end turn, your research occurs, followed shortly thereafter by CvCity::doReligion. The technology splash screen appears after all of this, at the beginning of your subsequent turn. With truly unfortunate timing (and rather dubious prioritization), you could theoretically find that – having founded a religion – you have a converted city (immediate spread from the holy city) but ruins where your holy city may have briefly stood (were it razed by one of the opposing players.[/indent]
Trade Network connected means almost what it sounds like; there must be a connection between the converted city and the holy city – that is, the cities must be part of the same plot group. Plot groups are determined by explicit routes (roads, railroads), and terrain routes (oceans, rivers, coastline). These latter types depend on which technologies have been discovered by the owner(s) of the cities. Why almost? Because cities can connect through a closed border.
Two factors determine the probability that the city will convert, given that it is connected to the holy city.
The first factor is plot distance, expressed as a percentage of the maximum possible plot distance on the map.
[indent]Two different distance terms are used in CIV. Step distance treats diagonals as one unit of distance. Plot distance treats them as roughly 1.5. When you watch a city expand its cultural borders, you are seeing it expand using plot distance[/indent]
In an unmodded game, you’ll observe about 10% per turn if you are in the immediate neighborhood of the holy city, falling off to 0.1% at the furthest corners of the map.
The second factor is the amount of influence the holy city has – the only building which affects the influence is the shrine, which doubles the probability that the religion will spread.
Although all of the religions are checked each turn, the test is interrupted if the city converts, so you will only see one spontaneous conversion in a city. The religions are checked in order, so there’s a probably-not-perceptible bias in favor of Judaism.
[i]Missionary Man, he’s got God on his side…[/i]
To deliberately spread a religion to a city, you may use a missionary to convert the city; this consumes the missionary. You can train the missionary in any city which has already converted to that religion if either of the following is true
[*]The city has constructed a monastery
[*]You are running the Organized Religion civic
Once the missionary has been trained, you simply move him to the target city, and click the convert action icon.
But… it doesn’t always work. If a city already has a religion, there’s some chance that the conversion will fail. The probability of failure increases linearly with the number of religions already in the city. You have better odds converting your own cities (about 9% chance of failure per previous religion), than those of other teams (the failure rate rises to almost 12% per).
For your own cities, the true conversion rates are (100%, 91%, 82%, 74%, 65%, 57%, 48%). Hooray for integer math.
Automated missionaries use a scoring algorithm to choose the city they will attempt to convert. Of some interest may be the fact that automated missionaries treat cities with no religions as though they had two religions for scoring purposes – therefore automated missionaries will prefer to convert cities with exactly one religion, all other things equal.
Complicating things further, the Theocracy civic is documented to “prevent the spread of non-state religions. Once again, this doesn’t quite mean what it says.
For spontaneous spreading, this is precisely right; your state religion is allowed to flow to one of your unconverted cities (if it is connected to the holy city), but no other religions may do so.
For missionary spreading, you prevent your opponents from spreading non-state religions to you, but you don’t prevent your teammates from doing so. You can always spread the religion yourself with your own missionaries, and your opponents can use their missionaries to spread your own state religion to you.
[i]To be continued[/i]
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