Members of Iran's dwindling Zoroastrian community are making their annual pilgrimage to the temple in the rocky mountain of Chakchak.
The temple is cut into the living rock of Chakchak mountain
The desert site near the central city of Yazd is holy to the minority whose numbers are said to have halved to 22,000 since the 1979 Islamic revolution.
It is believed the last Zoroastrian princess sheltered from the Muslims in a cave on Chakchak in AD640.
Yazd is the historic capital Zoroastrianism, considered by some to be the world's first monotheistic religion and a profound influence on Judaism, Christianity and Islam.
The faith was founded in about 600BC by the Persian prophet Zarathustra who believed he had seen visions of a God he called Ahura Mazda.
Zoroastrian rule was driven out of modern-day Iran by the Muslim Arab invasion 1400 years ago.
The last king Yazdgerd III was captured, but his second daughter Nikbanou escaped and is believed to have sheltered at Chakchak.
Legend says the Chakchak mountain opened up and received Nikbanou - closing behind her at a spot marked by a fresh water spring.
Pilgrims have long since removed a colourful rock believed to be a petrified cloth that was all that was left of Nikbanou.
Mountainous Chakchak houses one of Zoroastrianism's holiest sites
Today, pilgrims make their way up the towering rocks, following hundreds of steps to a cave where they pray and drink clear water from a spring.
Tea and wine are drunk inside - alcohol being allowed for religious use by non-Muslims in the Islamic republic. Women can also take off their obligatory veils.
As well as the deity, Zoroastrians also believe in a Satan-like figure, Aura Mainyu, and have their own holy book, the Avesta-E-Zend.
Zoroastrians are often mistakenly identified as fire-worshippers, perhaps from the presence of fires in their temples and the celebration of "the birthday of the fire" when they give thanks for the warmth and light afforded by fire.
Although certain Zoroastrian practices have been outlawed in Iran - leaving the dead to be eaten by vultures on "towers of silence", for example - Iranian tolerance apparently stems from the Persian roots of the religion.
The faith is recognised by Iran as an official religion
There is no basis for it in the Koran, but Zoroastrians are treated by Sunni Muslims too as People of the Book who are to be allowed to live in Muslim lands - like the Jews, Christians and Sabeans.
Nevertheless, centuries of persecution have forced many Iranian Zoroastrians to flee to India, where they are known as Parsis.
"We are a species on the road to extinction," Babak, a Tehran resident who has come to Chakchak for the pilgrimage, told the French news agency AFP.
But the tenets of the Zoroastrians' own faith - such as strict marriage laws - have also caused a decline in the population.