This ancient traditional festival honours and celebrates the element of fire, sacred in the Zoroastrian faith, and in so doing keeps at bay the spirits of darkness.
Like many other midwinter celebrations throughout the world, the Jashan e Sadeh festival used to be a channel through which human beings could assist the dying sun and revive it for the coming year. It is one of many ritual celebrations of the light that take place throughout the world around midwinter: a commentary, if you will, on the prevailing condition of being-freezing-cold-and-uncomfortable-and-wanting-to-warm-yourself-by-a-bonfire, a far too common condition during this time of the year.
The ancient Zoroastrians were also concerned with the threat of rampant demons of frost and darkness, led by the general of the army of darkness, Lord Ahriman, the eternal arch-enemy of the benign Creator Ahura Mazda. These two forces were locked in an eternal struggle between good and evil, darkness and light, and the outcome of the battle was affected by the actions of mere humans. Thus the bonfires served the dual purpose of warming the frozen members of the community and banishing the forces of darkness at the height of their campaign across the earth, when the days were at their shortest and the nights were long and freezing cold.
The ceremony was a ritual promise of fertility, as the demons of cold could turn the roots of plants into stone and kill off life from beneath the ground. To protect themselves and the earth, the Zoroastrians invoked the warming sun, in the figure of Lord Mihr, the great Immortal created by Ahura Mazda to watch over both the sun and the element of fire.
The celebrations traditionally centered around the sharing of a ritually blessed fire that was kept burning all night and day. This sacred element would travel from house to house on the torches of women and would be shared throughout the community. Other elements of the celebration were the ritual blessing of and saying of prayers for the dead, and the wood-gathering of boys that went from door to door asking for material for the fire. Evenings would be spent feasting and 'giving away good deeds' ('Khairat').
Sources conflict on the precise date of the celebration in Iran, but the consensus is that it takes place on the tenth day of the month of Bahman, ie 30 January. On this day a huge holy bonfire is lit in the street, with a flame from the fire temple, and there is chanting from sacred texts.