the conflict between good and evil.

The most prominent feature of the religion of Zarathustra is the
dual principle of good and evil and the conflict between them. Ahura
Mazda is the supreme deity, the creator of the world, and Ahriman or
Angro Mainyush is the evil one, his constant opponent. A perpetual
struggle proceeds between them, extending over the whole of creation,
and will continue for a period of 12,000 years. The virtuous lives and
prayers and sacrifices of men help the cause of Ahura Mazda, while
every bad action and all kinds of ceremonial impurity constitute an
assistance rendered by them to Ahriman. Not only virtue, courage,
charity humility and kindness to animals, when displayed by men,
are held to reinforce Ahura Mazda, but also such useful acts as
cleaning a field for cultivation, digging a canal or building a
bridge. The animals are also divided into good and bad, the latter
being considered the creation of Ahriman and designated the seed of
the serpent. The bad animals include tigers, snakes, cats, wolves,
frogs, mice, ants and others, and to kill them is to perform a
virtuous act in the cause of Ahura Mazda. Among good animals dogs
and agricultural cattle appear to be the chief. The division is very
imperfect, and it would seem that the classification does not extend
to birds and fish. Most trees are good, but their bark is evil. Hail,
snow and all kinds of diseases are believed to be the work of Ahriman
and his evil spirits. [357] As all ceremonial impurity renders
assistance to the evil one, the Parsis are very careful in such
matters, as will be noticed subsequently. Ahura Mazda is assisted
in his struggle for the good by six Amesha-Spentas or good spirits,
who are something like archangels. They consist of the spirits of
cattle, fire, metals, the earth, health and immortality. With the
first four of these some moral quality or attribute as truth, wisdom
and the curing of diseases is now associated. Another great spirit
Sraosha is the judge of the dead. Similarly Ahriman is assisted by six
arch-fiends and a whole host of evil spirits (Deva and Druj) of all
kinds, against whom men have to be perpetually on their guard. One
of the principal bad spirits is Aeshma Deva, the roaring demon, who
appears to be the Asmodeus mentioned in the Apocrypha. At the end
of the period of struggle Ahura Mazda will engage in a final contest
with Ahriman and will conquer with the help of the Archangel Sraosha,
who