There were no Castes

In the beginning, there were no castes (varna). (There are four castes- Brahmanas, kshatriyas, vaishyas and shudras. The Brahmanas are priests, the kshatriyas are kings and warriors, the vaishyas are agriculturists and traders, and the shudras are a serving class.) The Brahman was alone and the only caste that existed was that of Brahmanas. But the Brahman was not capable of performing all acts on his own. He therefore created gods like Indra, Varuna, Soma, Rudra, Parjanya, Yama, Mrityu and Ishana. These were the kshatryas among gods and there is no one who is superior to a kshatriya. It is for this reason that, in the course of a rajasuya sacrifice, the king is worshipped by Brahmanas. But kshatriyas were created from Brahmanas. And no matterhow supperior he may be, a king has to acknowledge the superiority of his place of origin, that is, Brahmanas. A kshatriya who slights a Brahmana insults his process of creation. A man who hates a superior being, brings destruction on himself. He is plagued by sin. Brahmanas must therefore be revered.
 "Upanishads"