My first discovery of the caste system was in the pages of the Bhagavad Gita. I have also read the Upanishads and a number of other ancient Indian cultural documents. (BTW, "Arabian Nights" also qualifies as such and I have read that.).
All of these Indian sources agree that there was a caste system and it has truly ancient roots. It continues into modern times. One of the ways out of the caste system is to become a Moslem. Another is to become a Sikh. Yet another is to become a Christian. It is a violation of Indian law to suggest to a Hindu of whatever caste that he become a Moslem, Sikh or Christian.
In India Protestant Christian missionaries have been murdered by being burned alive with burning motor vehicle tires within recent memory. They were murdered by Hindus.