One of my favorite things is that the most exalted level of holy fire in Zoroastrianism needs to be lit from combined and purified fires from all sorts of fire-usage

And that one of the sources is a cremation fire, but Zoroastrians are bound from being cremated (as it’s degrading to the fire; they’re traditionally associated with sky burial)

Which means the sanctification of the highest temples requires the sponsorship of non-Zoroastrians