The "Sadeh festival" is the largest fire celebration and one of the oldest known traditions in ancient Persia, which is celebrated forty days after the Yalda Night as thanksgiving from God's blessings by Zoroastrians.
This celebration is a sign of the importance of light, fire and energy in life, which begins with setting the fire on the top of mountains and roofs of houses near the sunset of the tenth of Bahman. The Sadeh festival is one of the great Iranian celebrations with no religious aspect and all the stories related to it are non-religious. This celebration would has been held by the kings, emirs and ordinary people from the pre-Islamic period, the Islamic era, until the late Khwarazmian era and the Mongol conquest and has continued to this day. There have been various narratives and opinions about the naming of the Sadeh and setting the fire. The most famous and largest celebrations of the Sadeh festival are held in Isfahan in Mardavij era when he celebrated the Sadeh and was killed at the end of the celebration by his opponents in 323 AH.
Sadeh celebration is held in many cities and villages of Iran and by Zoroastrians residing in other countries with the gathering and the presence of Zoroastrian, Muslim, and Persian Jews and etc., in one place, with the establishment of a large fire outside the city and the implementation of the different programs. Ancient Persians was on this belief that the Zoroastrians are gathered around a great fire and this fire bring warmth and light, and keeps fresh the hope for the triumph of light on darkness in the hearts. People gather together in the collecting of firewood from the days before the celebration. Today, According to the custom of this magnificent celebration in many regions of Iran despite the passing of thousands of years since the first Sadeh, no significant changes have been made in this celebration.