You can also ask another player to stop preaching in your cities, if you want. The base range is 10 (14 with itinerant preachers), and is not dependent on roads/terrain. Each Religious City will send out +6 pressure for its Religion to all Cities within a 10-tile range. The Great Mosque of Djenne will make all Missionaries born in a City have 3 Convert actions instead of 2, and there are a number of Beliefs that can affect Conversions - such as making Missionaries capable of wearing away other Religious Pressure like Great Prophets (Evangelism).Without any other Religion competing, it takes 100 Pressure to convert 1 Citizen to follow a Religion. Odds are, Itinerant Preachers (13-hex pressure) or Religious Texts (Religion Spreads 25% faster, 50% with Printing Press) will be your top choices if you want your Religion spread globally. While a couple of Civs get direct bonuses to Faith generation, all will need higher amounts of Faith to effectively utilize Religion.
Generally, no, it is impossible to bring a religion back from that level of elimination.
This gradually wears them down until they disband, their conversion strength diminishing with each turn passed in foreign lands. Just as in the real world, Religion consists of a series of Beliefs, which define the religion's ideas and goals. You can only choose any of the beliefs that no other religions have.These beliefs provide additional empire-level bonuses that may help you in spreading your Religion. At any rate, you should have already a solid core of cities with your religion, which will create a critical mass of religious pressure which spreads naturally, so you don't have to worry too much about it.
However, if you still have control of your religion's Holy City, and you managed to completely isolate it from other religions so that there is no pressure from them, then your religion would restore itself in that city.
Of course, the earlier you found and enhance your Religion, the more Beliefs you'll be able to choose from. You may choose one of these beliefs only when the Religion enhances.Beliefs are the practical effects of religions and pantheons, selected when they are founded or enhanced. Use this to get your Religion "behind enemy lines" so to speak and allow you to convert more Cities. Sea Trade routes are good as well, given they start with 20-tile ranges and can go to 45, while giving more gold than land trade routes.Keep in mind that using Remove Heresy on a Holy City will not remove the Religion from the game, but merely stop that City from exerting pressure. On standard time/size: The holy city auto influence itself with 30 pressure per turn Every city in range of a converted city receive 6 pressure per turn (8/10 with Religious texts) from this city. Faith is the resource that drives the Religion system in Civ 5 Gods and Kings. Use later opportunities to change Trade Routes up and get them to Cities that will help spread your Religion in another part of the map. Most Beliefs' effects only work on city level, so you will only benefit from them if your (and other) cities convert to your religion. In short, the more cities worldwide follow your religion, the better for you! If a city has a majority religion (i.e. You can choose one of these beliefs when founding a Religion. Converting the other Cities with a Great Prophet or Missionaries would be necessary to remove it from the game entirely. Please note that there is also an additional Bonus Belief, exclusive to Byzantium, increasing the number of beliefs to six.