India's caste system is believed to have originated with the Aryan invasion in the first millennium B.C. and has been a part of Hindu culture ever since, according to Faithology. The caste system has four parts--Brahmins, Kshatriyas, Vaishyas and Shudras. Another part of Hindu society are the Dalits, or untouchables, who were not part of any caste.
The caste system is mentioned in the Rig Veda, the Aryan holy text, when it speaks of Purusa, the first human being who was sacrificed to become the four castes (varnas). The mouth of Purusa is the Brahman caste, the two arms were Kshatriyas, the two legs were Vaishyas and the feet became Shudras. The first of these texts were published between 1500 and 1000 B.C.
The Brahmins consisted of priests who were responsible for the ritual functions of the Aryan religion. Kshatriyas were kings and warriors. Vaishyas were the class of farmers, merchants, artists and other skilled professionals. Shudras made up the servant and lowest class of the caste system. Shudras served the other three castes.
Traditionally, no one from one caste could marry into another. No one could elevate from one caste to another during a lifetime. Discrimination due to traditional castes is illegal in India. Modern Hindus determine castes by birth.