Zurvanism, modified form of Zoroastrianism that appeared in Persia during the Sāsānian period (3rd–7th century ad). It was opposed to orthodox Zoroastrianism, which by that time had become dualistic in doctrine. According to Zurvanism, time alone—limitless, eternal, and uncreated—is the source of all things.
Zurvān, god of time and fate, remotely influences human destinies, appearing under two aspects: Limitless Time (i.e., eternal lord; Zurvān Akarana) and Time of Long Dominion (i.e., lord of the existing world; Zurvān Dareghō-Chvadhāta). His worship is bound up with speculations about astrology and the world-year. He bears the epithets ashōqar, frashōqar, and zarōqar (meanings disputed), and the qualities these apparently indicate were construed as concrete, Zurvān being worshipped in four forms.
In later writings Zurvān is seen as the father of Ormazd and Ahriman (see Ahura Mazdā), perhaps a result of contact between Zoroastrianism and Greco-Babylonian astrological speculations. (Zurvanism appears to have had its stronghold in western Persia, bordering Babylonia.) Some scholars seek an origin for Zurvanism outside Zoroastrianism, in the worship of an ancient Median or pre-Iranian god. Although in its fatalism and pessimism Zurvanism is basically opposed to true Zoroastrianism, it seems probable that in cult and in a large body of doctrine it made few breaks with orthodoxy. It was in Zurvanite form that Zoroastrianism influenced Mithraism (in which Zurvān was an important deity) and Manichaeism.