I came across this book, by accident, but it fasinated me. The author was inspired by Genisis 61.4 in the Jewish old testement. "It was then, and later too, that the Nephilim appeared on earth when thw devine beings cohabited with the daughters of men, who bore them offspring. They were the heroes of old, the men of renown."
He also was inspired by Von Daniken, and his books, as well, the series "Ancient Aliens" that was on TV. His research, will open you to also wonder about the orgin of mankind on earth as well possible "alien influence!"
It is available from Amazon, you can order one or many. It will open your mind as to our world, and "what's out there!!" I am not sure if the price I quote is correct, it may be less. Check with Amazon.