The Spread Culture Espionage Mission some ideas for using it.
Synopsis: This mission is a powerful tool in the hands of an espionage economy. It can help with rapidly recovering cities after conquering them. It can even be used to make a legendary city as part of a cultural victory. It can be chain linked over many cities spreading the effect to cities not normally targetable. It can massively reduce the cost of other espionage missions. There are many reasons to understand what this mission can do.
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Recently Ive been trying to find a use for this mission. It has usually been written off as useless or unusable by most commentators trying to make sense of the Espionage System, but in that case it has been seriously misunderstood. I suppose that might be because it is required to understand how the espionage system works and how the culture system - and both are complicated.
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First lets define a few terms that Ill be using, otherwise what I say might not make sense.
City Culture (CC): The total culture in a city. It increases each turn by the amount of culture per turn. When it reaches certain values the city borders pop (10, 100, 500, 5000 and 50,000 are values for border pops at normal speed). When a city is captured the CC value is retained and if recaptured starts from where it left off. It is possible for 3 or 4 civs to have its own CC value for a city.
Culture per turn (Cpt): This is a value the player can manipulate by constructing cultural buildings, wonders, running artist specialists or raising the cultural slider. It consists of a base culture and has several multipliers including cathedrals and Free Speech.
Tile Culture (TC): The value of a civs culture in a tile. Each turn a city adds culture to the surrounding tiles inside its borders. The amount added is Cpt plus a bonus of 20 for every zone (or border pop). So tiles close to a city get a bigger bonus and also they have been accumulating the culture for a longer period. More than one city can add TC to a tile in a turn. It is TC that determines who controls a tile. To be under control the tile needs to be inside the border of at least one of the city of its civ and to have the highest TC. Another civs might have higher TC in the tile but it is not within their borders and so outside their control. Yet another civ might have borders that extend over the tile but the TC is not high enough.
Spread Culture: A spy mission that adds 5% culture to the CC of a city. It has a base cost of 3 EPs per culture added to the city. But this base cost is modified by all the normal spy modifiers including a penalty for distance from capital, a -10% for each turn the spy is stationary, state religion modifier, trade route modifier, security bureau, total espionage spending and CCM (see next).
City Culture Modifier (CCM): There is also an additional espionage modifier that depends on your CC in that city. And the way you increase that is by running multiple missions. The more culture thats added the better the discount you get for this and other missions. So if you want to steal techs on the cheap run a few Spread Culture missions first.
[Incidentally, Im not sure of its exact value but it seems to be a ratio of your CC in the city versus the CC of the current owner of the city. Perhaps someone can dig into the code for the precise value.]
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Many players using the Spread Culture mission expect it to affect the TC, but is doesnt, it affects the CC instead. In fact it is the only way to increase the CC of a city when you do not control the city. But because it doesnt affect the TC directly most players think its useless.
The secret is that you need to use the Spread Culture mission and then capture the city. When it comes out of revolt that city then starts with whatever culture you managed to inject.
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When can you use the Spread Culture mission?
This also causes confusion because you can only use it in cities that are in range of the culture from another of your cities. On border areas this means that you need to get border pops such that you are putting culture into the city tile of the target city. Then you can start running the mission.
Mission Costs:
The amount of culture added by the mission is always 5% of the total of all the current CCs from all players (including yourself). So the base cost can escalate as you run your missions and add more and more culture to your CC or it can increase as the city develops under its current owner. Sometimes it might be better to wait a while for the owners CC to grow so that fewer missions are needed, which will reduce spy losses and needs less management. Also waiting can allow time for a bigger EP spending discount to be built up or for you to add your state religion to the city.
Chaining Cities valid cities:
Actually you dont need to have the target city in cultural range of one of your own cities. You are not limited to the enemy border cities. Once youve built up the CC of a target city it also counts as a virtual source of your culture (although TC is not generated of course). Remember the Spread Culture mission works on the CC. It seems that the Spread Culture mission is available based only on whether you have a city with a high enough CC. So you can either increase the CC of your own cities by adding Cpt until the border pops, OR you can increase the CC of an enemy owned city using the Spread Culture mission. In that way you can construct a chain of cities deep into enemy culture. If enemy cities are 3 tiles apart you need 500 CC to bridge the gap.
How to use it for conquest:
One of the great problems with late game warmongering is capturing a large number of cities which have been in place since the beginning of the game. Unless you can wipe the other civ out Motherland can be a serious problem. Even if you do wipe out the civ, so all his culture is removed, the neighbours culture can be a serious problem. It takes a long time to build up 500 culture if you have to start from zero and can only add one building a turn. The alternative of a few Spread Culture missions raising the CC to 500 before the city is taken makes this situation a lot easier to handle.
Making a Legendary City:
This is an interesting twist on how to get a cultural victory. Instead of getting 3 cities up to 50,000 culture using the traditional ways - I wont detail these but there are good threads and discussions on these forums you can use the Spread Culture mission to raise the CC on one (or even two) target cities that you simply capture and they become Legendary as soon as they come out of revolt. So you might make 2 Legendary cities the traditional way (and use any Great Artists to boost these at the end) and then use your EPs to get the third city to Legendary.
To make a legendary city the normal way requires a great deal of effort in that city, constructing wonders and buildings (particularly cathedrals) and then spends many turns gaining 500 to 1000 culture. Note other cities cant help raise the CC of these (soon to be) legendary cities directly. They can help, indirectly, by raising gold, spreading religions, building the 3 temples needed for each cathedral and making enough troops to defend the legendary city. The limitation on a cultural victory is usually how quickly you can get your third city there. By only having to raise 2 Legendary cities that means unique buildings such as wonders and national wonders can be shared between two rather than 3 cities and a lot less temples and cathedrals are needed and importantly any Great Artists only need to be shared between the 2.
Using the Spread Culture mission means that all your cities can help with making the EPs and building spies. So having a lot of cities is useful and they can directly affect the target city. Also you can very rapidly turn a city Legendary if you have enough EPs stockpiled and enough spies ready to run the missions (I guess the survival rate is about 80%). If the capital is close (move it, if its not) and you have railways the spies are in the target city every turn. They can start there, perform their mission and return to the capital, then next turn they move back, and after that they wait a few turns until the desired discount is built up.
As mentioned before, the base cost of raising the CC is 3 EPs per culture point. But with the discounts (including the City Culture modifier) and the large espionage spending advantage means that you are effectively paying 1 EP for 1 culture. Failed missions cost a spy and do not lose the EPs. A spy is only 40 hammers and at this stage of the game, in the Renaissance or Industrial ages, many cities can build one per turn with a hammer overflow (which generates cash). Another huge advantage is that once you have the EPs and spies stockpiled you can add many 1000s of culture to the target city CC each turn (I think my record is 12,000 in the last turn). This is far more rapid than with normal culture. Only a great artist culture bomb which adds 4000 to the CC can get close to a well orchestrated set of Spread Culture missions. You could even combine the approaches and use a spare great artist to finish off a city that hadnt quite made 50,000 CC.
In fact a hybrid approach is possible, although Ive not tried it yet. You could say have your capital which has a lot of wonders and has been going a long time and that will be one legendary city. Just leave that to cook away in the background. Then you see a good target city (perhaps with lots of fully developed towns) all it needs is to be on your side and some cathedrals and some turns. So you dump whatever EPs you have build up at that stage into Spread Culture missions (say 30,000 EPs) and capture the city. So it starts with 30,000 CC and has a much more manageable task despite a late start. Now use US to rush buy some good culture modifiers and when the time is right turn up the cultural slider. Meanwhile the rest of your cities are building up a huge stockpile of EPs and spies for the third city.
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Closing remarks:
Those are the things I've discovered and ideas Ive had in the last few days while developing these strategies. Im sure many of you can come up with better ways to use this idea in ways I cant imagine. Id like to hear your comments.
I might edit this OP in light of comments.
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[Disclaimer: I have not yet updated my BtS to the latest patch as I had many games to finish. The tests and all information given above are correct for the Bhruic patch. However, I do not expect the aspects of the game discussed here to be significantly changed as it was not mentioned in the changes list. I will update my BtS to the latest patch in a week or two.]
Synopsis: This mission is a powerful tool in the hands of an espionage economy. It can help with rapidly recovering cities after conquering them. It can even be used to make a legendary city as part of a cultural victory. It can be chain linked over many cities spreading the effect to cities not normally targetable. It can massively reduce the cost of other espionage missions. There are many reasons to understand what this mission can do.
-----------------------
Recently Ive been trying to find a use for this mission. It has usually been written off as useless or unusable by most commentators trying to make sense of the Espionage System, but in that case it has been seriously misunderstood. I suppose that might be because it is required to understand how the espionage system works and how the culture system - and both are complicated.
-----------------------
First lets define a few terms that Ill be using, otherwise what I say might not make sense.
City Culture (CC): The total culture in a city. It increases each turn by the amount of culture per turn. When it reaches certain values the city borders pop (10, 100, 500, 5000 and 50,000 are values for border pops at normal speed). When a city is captured the CC value is retained and if recaptured starts from where it left off. It is possible for 3 or 4 civs to have its own CC value for a city.
Culture per turn (Cpt): This is a value the player can manipulate by constructing cultural buildings, wonders, running artist specialists or raising the cultural slider. It consists of a base culture and has several multipliers including cathedrals and Free Speech.
Tile Culture (TC): The value of a civs culture in a tile. Each turn a city adds culture to the surrounding tiles inside its borders. The amount added is Cpt plus a bonus of 20 for every zone (or border pop). So tiles close to a city get a bigger bonus and also they have been accumulating the culture for a longer period. More than one city can add TC to a tile in a turn. It is TC that determines who controls a tile. To be under control the tile needs to be inside the border of at least one of the city of its civ and to have the highest TC. Another civs might have higher TC in the tile but it is not within their borders and so outside their control. Yet another civ might have borders that extend over the tile but the TC is not high enough.
Spread Culture: A spy mission that adds 5% culture to the CC of a city. It has a base cost of 3 EPs per culture added to the city. But this base cost is modified by all the normal spy modifiers including a penalty for distance from capital, a -10% for each turn the spy is stationary, state religion modifier, trade route modifier, security bureau, total espionage spending and CCM (see next).
City Culture Modifier (CCM): There is also an additional espionage modifier that depends on your CC in that city. And the way you increase that is by running multiple missions. The more culture thats added the better the discount you get for this and other missions. So if you want to steal techs on the cheap run a few Spread Culture missions first.
[Incidentally, Im not sure of its exact value but it seems to be a ratio of your CC in the city versus the CC of the current owner of the city. Perhaps someone can dig into the code for the precise value.]
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Many players using the Spread Culture mission expect it to affect the TC, but is doesnt, it affects the CC instead. In fact it is the only way to increase the CC of a city when you do not control the city. But because it doesnt affect the TC directly most players think its useless.
The secret is that you need to use the Spread Culture mission and then capture the city. When it comes out of revolt that city then starts with whatever culture you managed to inject.
-----------------------
When can you use the Spread Culture mission?
This also causes confusion because you can only use it in cities that are in range of the culture from another of your cities. On border areas this means that you need to get border pops such that you are putting culture into the city tile of the target city. Then you can start running the mission.
Mission Costs:
The amount of culture added by the mission is always 5% of the total of all the current CCs from all players (including yourself). So the base cost can escalate as you run your missions and add more and more culture to your CC or it can increase as the city develops under its current owner. Sometimes it might be better to wait a while for the owners CC to grow so that fewer missions are needed, which will reduce spy losses and needs less management. Also waiting can allow time for a bigger EP spending discount to be built up or for you to add your state religion to the city.
Chaining Cities valid cities:
Actually you dont need to have the target city in cultural range of one of your own cities. You are not limited to the enemy border cities. Once youve built up the CC of a target city it also counts as a virtual source of your culture (although TC is not generated of course). Remember the Spread Culture mission works on the CC. It seems that the Spread Culture mission is available based only on whether you have a city with a high enough CC. So you can either increase the CC of your own cities by adding Cpt until the border pops, OR you can increase the CC of an enemy owned city using the Spread Culture mission. In that way you can construct a chain of cities deep into enemy culture. If enemy cities are 3 tiles apart you need 500 CC to bridge the gap.
How to use it for conquest:
One of the great problems with late game warmongering is capturing a large number of cities which have been in place since the beginning of the game. Unless you can wipe the other civ out Motherland can be a serious problem. Even if you do wipe out the civ, so all his culture is removed, the neighbours culture can be a serious problem. It takes a long time to build up 500 culture if you have to start from zero and can only add one building a turn. The alternative of a few Spread Culture missions raising the CC to 500 before the city is taken makes this situation a lot easier to handle.
Making a Legendary City:
This is an interesting twist on how to get a cultural victory. Instead of getting 3 cities up to 50,000 culture using the traditional ways - I wont detail these but there are good threads and discussions on these forums you can use the Spread Culture mission to raise the CC on one (or even two) target cities that you simply capture and they become Legendary as soon as they come out of revolt. So you might make 2 Legendary cities the traditional way (and use any Great Artists to boost these at the end) and then use your EPs to get the third city to Legendary.
To make a legendary city the normal way requires a great deal of effort in that city, constructing wonders and buildings (particularly cathedrals) and then spends many turns gaining 500 to 1000 culture. Note other cities cant help raise the CC of these (soon to be) legendary cities directly. They can help, indirectly, by raising gold, spreading religions, building the 3 temples needed for each cathedral and making enough troops to defend the legendary city. The limitation on a cultural victory is usually how quickly you can get your third city there. By only having to raise 2 Legendary cities that means unique buildings such as wonders and national wonders can be shared between two rather than 3 cities and a lot less temples and cathedrals are needed and importantly any Great Artists only need to be shared between the 2.
Using the Spread Culture mission means that all your cities can help with making the EPs and building spies. So having a lot of cities is useful and they can directly affect the target city. Also you can very rapidly turn a city Legendary if you have enough EPs stockpiled and enough spies ready to run the missions (I guess the survival rate is about 80%). If the capital is close (move it, if its not) and you have railways the spies are in the target city every turn. They can start there, perform their mission and return to the capital, then next turn they move back, and after that they wait a few turns until the desired discount is built up.
As mentioned before, the base cost of raising the CC is 3 EPs per culture point. But with the discounts (including the City Culture modifier) and the large espionage spending advantage means that you are effectively paying 1 EP for 1 culture. Failed missions cost a spy and do not lose the EPs. A spy is only 40 hammers and at this stage of the game, in the Renaissance or Industrial ages, many cities can build one per turn with a hammer overflow (which generates cash). Another huge advantage is that once you have the EPs and spies stockpiled you can add many 1000s of culture to the target city CC each turn (I think my record is 12,000 in the last turn). This is far more rapid than with normal culture. Only a great artist culture bomb which adds 4000 to the CC can get close to a well orchestrated set of Spread Culture missions. You could even combine the approaches and use a spare great artist to finish off a city that hadnt quite made 50,000 CC.
In fact a hybrid approach is possible, although Ive not tried it yet. You could say have your capital which has a lot of wonders and has been going a long time and that will be one legendary city. Just leave that to cook away in the background. Then you see a good target city (perhaps with lots of fully developed towns) all it needs is to be on your side and some cathedrals and some turns. So you dump whatever EPs you have build up at that stage into Spread Culture missions (say 30,000 EPs) and capture the city. So it starts with 30,000 CC and has a much more manageable task despite a late start. Now use US to rush buy some good culture modifiers and when the time is right turn up the cultural slider. Meanwhile the rest of your cities are building up a huge stockpile of EPs and spies for the third city.
-----------------------
Closing remarks:
Those are the things I've discovered and ideas Ive had in the last few days while developing these strategies. Im sure many of you can come up with better ways to use this idea in ways I cant imagine. Id like to hear your comments.

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[Disclaimer: I have not yet updated my BtS to the latest patch as I had many games to finish. The tests and all information given above are correct for the Bhruic patch. However, I do not expect the aspects of the game discussed here to be significantly changed as it was not mentioned in the changes list. I will update my BtS to the latest patch in a week or two.]