Nowruz is partly rooted in the tradition of Iranian religions, such as Mithraism and Zoroastrianism. In Mithraism, festivals had a deep linkage with the Sun's light. The Iranian festivals such as Mehrgan (autumnal equinox), Tirgan, and the eve of Chelle ye Zemestan (winter solstice) also had an origin in the Sun god (Surya). Among other ideas, Zoroastrianism is the first monotheistic religion that emphasizes broad concepts such as the corresponding work of good and evil in the world, and the connection of humans to nature. Zoroastrian practices were dominant for much of the history of ancient Iran. In Zoroastrianism, the seven most important Zoroastrian festivals are the six Gahambar festivals and Nowruz, which occurs at the spring equinox. According to Mary Boyce, "It seems a reasonable surmise that Nowruz, the holiest of them all, with deep doctrinal significance, was founded by Zoroaster himself"; although there is no clear date of origin. Between sunset on the day of the sixth Gahambar and sunrise of Nowruz, Hamaspathmaedaya (later known, in its extended form, as Frawardinegan; and today known as Farvardigan) was celebrated. This and the Gahambars are the only festivals named in the surviving text of the Avesta.