Related: Stark Truth About Aryans: a story of India and Stark Truth About Humans: a story of India.
In 1030 AD, the Muslim ethnographer al-Biruni completed Indica, the first work of anthropology about the Indian subcontinent by an outsider. Commenting on the social structure of South Asia, he wrote:
The Hindus call their castes varna, i.e., colors, and from a genealogical point of view they call them jataka, i.e. births. These castes are from the very beginning only four.
I. The highest caste are the Brahmana...
II. The next caste are the Kshatriya...Their degree is not much below that of the Brahmana.
III. After them follow the Vaisya, who were created from the thigh of the Brahman.
IV. The Sudra, who was created from his [Brahma] feet…
Clearly, already 1,000 years ago outsiders could readily discern the broad lineaments of Indian social structure. But even al-Biruni had much earlier predecessors. In 300 BC, Greek historian Megasthenes was an ambassador at the court of Chandragupta Maurya, the ruler of most of India. He too contributed a work entitled Indica, and observed that there were seven hereditary and endogamous occupational groups in India, with the most esteemed being the “philosophers.”