They're the feet, the laborers and the farmers, who are the foundation of the social order. Also, the rest of us stand on them. The caste system becomes much more complicated than this, but that basic division into four classes remains throughout much of Indian history. In spite of the efforts of many reformers we'll be meeting in future episodes of Crash Course, the caste system is the foundation for another big concept in Hinduism, Part Three, Dharma. Dharma is basically one's role in life and society, and it is defined primarily by birth and by caste. This whole idea is explained nicely in this passage from the Bhagavad Gita, where Krishna is talking to the warrior Arjuna. "...having regard to your own duty also, you ought not to falter.