Over time, a place that is used for religious ceremonies takes on a certain significance. Not simply in the minds of the followers of that religion, but also in others who pass through an area.
In the oldest groves and shrines of the world, the presence of those ancient, gloomy gods can still be felt. In the shining altars of Mitra or the bloody slabs of Set, the manifestation of this spiritual presence is palpable.
When a shrine is defiled, this effect leeches slowly away, but if the defilers are of an opposing religion, they actually absorb the power that they have stolen. Thus altars are a precious commodity in the Exiled Lands and worship brings great bounties to those who pursue it.