keeping all religions to yourself.

[lordrune]

Yeah Asmodeus.

I think you'd actually have to build your civ with no road connections to water, apart from any landlocked lakes you can find and encircle within your cultural borders.

Quite a fascinating challenge concept actually

Could all be a moot point if religion does in fact expand outside your civ even if no connections exist.

edit - and make sure you don't build any airports

[VoiceOfUnreason]

The game mechanic is that only cities which are connected to the holy city are eligible for "automatic conversion" [see CvCity::doReligion].

The implication is that if you isolate the holy city (cities), you can connect your other cities, and spread your hoarded religions to them, without concern that they will leak across the borders.

(Disclaimer: that covers the automatic spread of religions. To my knowledge, there is no "steal religion" spy mission, but I haven't looked too closely).

This game mechanic was used to elegant effect in Pilgrimage to Mecca; a challenge game reported in Another Place[tm].


If you insist on connecting your holy cities to the rest of your civ, you can still maintain a monopoly on religions by ensuring that you are at war with all civs that share your trade borders (which in particular means that you need to be in "always war" mode once you hit Astronomy).

Edit: unless I've misread the code by a whole lot, airports don't matter at all.

[Blake]

War is only good in an emergency, or if you've met everyone. Religion can still spread to people you haven't met yet - if there is a valid route through others player's territory.

[joncnunn]

In order for this to work the entire game you'd have to have no coastal cities nor any river cities and in addition never build a road that touches a river nor a coastal tile.
I don't think that's a good idea because to result in too many sub par city locations and unconnected resources.
(Technically you could just isolate all the holy cities, but until you reach Islam you don't know which existing city will be chosen. And even then if the holy cities had no connections they are going to have major healthiness problems.)

If your only objective is pre-Astronomy, then you could take sole possesion of your landmass plus any landmasses so close that you could reach them with Galleys. If you pick an Archepello this might be possible.