Sky And Earth

"Sky Father's worshippers still feared the earth gods for whom, further inland, a human being was devoured every harvest."
-Poul Anderson, The Corridors Of Time, CHAPTER NINE, p. 75.

This is a transitional stage in the history of religion. Sky Father is becoming the one God and the earth gods are becoming demons.

Hindu gods and demons are devas and asuras, respectively. When two Aryan groups parted company, each regarded the other's gods as demons. Thus, devas became devils and the one God of Zoroastrianism is Ahura Mazda.

Poul Anderson's time travelers, both in his Time Patrol series and in The Corridors Of Time, are able to immerse themselves in prehistoric periods to an extent that is impossible for historians living at a later date. See "Manse Everard's Religious Experiences," here. Although Everard wants to escape from the alienness of Cyrus' period, many later scholars would welcome the opportunity to experience it in full.