Long before Christianity or Islam existed, Zoroastrianism, one of the world's oldest monotheistic faiths, was one of the most dominant religions on Earth for about 1,000 years.

With about 200,000 followers, most of whom live in India or Iran, identifying themselves as Zoroastrian today, the religion still has a sizeable following even if it is dwarfed by the world's big three monotheistic religions.

What exactly is Zoroastrianism, and what do its adherents believe? Today's Seeker Daily video answers those questions.

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Founded by the prophet Zoroaster in the sixth century B.C., Zoroastrianism follows a single god, known as Ahura Mazda, a name that translates to "wise lord." Ahura Mazda is a benevolent, omniscient, omnipotent and omnipresent creator deity who designed a "perfect" universe.

Zoroastrians also believe in dualism, or a world in which everything exists within moral opposites. The opposite of Ahura Mazda, for example, is Angra Mainyu, which translates to destructive spirit. Just as Ahura Mazda is the source of life and goodness in the world, according to Zoroastrians, Angra Mainyu brings death and evil to the world. This duality is reflected in Christianity and Islam, and in fact that concept of heaven, hell and the devil are largely inspired by Zorostrian dogma.

Followers of Zoroastrianism believe that "good thoughts, good words and good deeds" keep evil at bay. The "law of Asha" is a prescription for those looking to follow a righteous path. There isn't a strict moral code or long list of rules, unlike other monotheistic faiths.

Zoroastrianism also differs from other religions with its emphasis on individual, rather than group worship. Members of the faith only ever gather together to celebrate their religion during holidays or other special occasions.

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Although Zoroastrianism flourished thousands of years ago, it has seen the number of followers decline precipitously in the modern era, largely as a result of oppression, forced conversions and migrations.

In Iran, where the religion was founded, Zoroastrians are routinely persecuted and subject to "increasing repression and discrimination," often subject to intimidation and arrests, according to the United States Commission on International Religious Freedom. India, home to more Zoroastrians than anywhere else on Earth, loses about 10 percent fewer followers every decade.

Zoroastrians once numbered in the tens of millions, but today they are a rare find, and someday, they might only turn up in the history books.

-- Talal Al-Khatib

Learn More:

Washington Post: Saudi Arabia's Top Cleric Says Iran's Leaders 'Not Muslims'

BBC: Zoroastrianism at a Glance

NPR: Zoroastrianism an Ancient, Shrinking Religion