Mehregan, or Mehr Celebration or Autumn Nowruz, was linked to the Autumnal Equinox, when day and night became equal in length. The celebration was held in the first days of autumn and usually lasted a few days.
As it is told, the main index for celebrating Mehregan was when day and night became equal, just as Nowruz is the celebration of the spring equinox. Therefore, Mehregan is known as the second biggest celebration in the Iranian calendar and has a high value in Iranian culture. The day was celebrated on Oct. 2 by ancient Zoroastrians, but Oct. 8 has also been mentioned as the day of Mehregan in some sources.
Mehregan celebration is actually the celebration of crop harvest and thanksgiving for natural gifts and the victory of goodness over badness.
Etymology of Mehregan
The root of Mehr in Mehregan goes back to an Indo-European common word “Mitra.” The word has been mentioned in the Avesta – the holy book of Zoroaster – in the form of Izad Mitra [Izad means goddess].
Mehr or Mitra in Persian means “light, friendship, bond, and kindness, and it is the opposite of lying, breaking promises, and unkindness.
Many translate Mehr as “love and friendship,” not “deal or contract,” because what finds meaning among families is “love and friendship,” not “deal or contract.” Mehr has been used in the meaning of light and sun as well. Mitraism was spread across Rome since the beginning of the 1st century A.D., according to the images remaining from that period of time.
Mehregan as myth
Iranian well-known poet Ferdowsi has mentioned the day Mehregan in the Book of Kings “Shahnameh”, as a day that Fereidoon ascended to the throne.
Most historians have also said that Mehregan was a day when Fereidoon overcame Zahak and chained him on the summit of Damavand. Some Iranian Zoroastrians believed that it was a day when Fereidoon sacrificed a sheep or goat and ordered people to do so. Poor families sacrificed a chicken instead. However, it is not a universal narrative among all Zoroastrians.

Modern Iran also celebrates Mehregan
The ceremony of Mehregan will be celebrated across Iran on Oct. 10, according to the deputy of Cultural Heritage, Handicrafts, and Tourism Organization.
Ali Darabi has said that the celebration will be held with the aim of introducing the ancient ceremonies to the young generation and creating a happy ambiance filled with social dynamism for families. He said that the main objectives of these ceremonies are to improve the unity between nationalism and religion, safeguard spiritual heritage and link it to everyday life, as well as help improve tourism.
The most important centers where Mehregan is celebrated in Iran
Mehregan is celebrated in the provinces of Yazd and Kerman with greater splendor, as these two cities host more Zoroastrians and fire temples. However, the celebration is also held in other cities, including Tehran, since Iranians attach great importance to their national identity and see these events as a sign of unity.