Only nine Atash Behram, fires of the highest grade, exist anywhere in the world, and the smallness of that number is itself a record of Zoroastrian history. Consecrating one requires assembling and ritually uniting sixteen separate fires gathered from different sources, among them a fire struck by lightning and a fire taken from the hearth of a corpse-bearer, a process that can take close to a year of ceremony to complete, which is why so few have ever been established at all.
Eight of the nine stand in India, chiefly in Gujarat and Mumbai, founded by the Parsi community descended from Zoroastrians who left Iran for India between roughly the eighth and tenth centuries to escape pressure following the Islamic conquest of Persia, carrying their religious practice into a new country where it has continued protected ever since.
The ninth, the Yazd Atash Behram in Iran, tends a fire its custodians trace back some fifteen hundred years, and the small Zoroastrian community remaining in Iran, a fraction of its pre-Islamic numbers, maintains it under conditions considerably more constrained than those of their Indian co-religionists. Both Iranian and Indian fire temples restrict entry to Zoroastrians alone, a rule the Parsi community in particular enforces strictly and has defended in Indian courts against occasional legal challenge, on the ground that a fire ritually purified through such an exacting process must remain undisturbed by the presence of those outside the faith it was consecrated for.