A series of migrations by Indo-European-speaking seminomads took place during the second millennium B.C. Known as Aryans, these preliterate pastoralists spoke an early form of Sanskrit, which has close philological similarities to other Indo-European languages, such as Avestan in Iran and ancient Greek and Latin. The term Aryan meant pure and implied the invaders' conscious attempts at retaining their tribal identity and roots while maintaining a social distance from earlier inhabitants.
Although archaeology has not yielded proof of the identity of the Aryans, the evolution and spread of their culture across the Indo-Gangetic Plain is generally undisputed (see Principal Regions, ch. 2). Modern knowledge of the early stages of this process rests on a body of sacred texts: the four Vedas (collections of hymns, prayers, and liturgy), the Brahmanas and the Upanishads (commentaries on Vedic rituals and philosophical treatises), and the Puranas (traditional mythic-historical works). The sanctity accorded to these texts and the manner of their preservation over several millennia--by an unbroken oral tradition--make them part of the living Hindu tradition.
These sacred texts offer guidance in piecing together Aryan beliefs and activities. The Aryans were a pantheistic people, following their tribal chieftain or raja, engaging in wars with each other or with other alien ethnic groups, and slowly becoming settled agriculturalists with consolidated territories and differentiated occupations. Their skills in using horse-drawn chariots and their knowledge of astronomy and mathematics gave them a military and technological advantage that led others to accept their social customs and religious beliefs (see Science and Technology, ch. 6). By around 1,000 B.C., Aryan culture had spread over most of India north of the Vindhya Range and in the process assimilated much from other cultures that preceded it (see The Roots of Indian Religion, ch. 3).
The Aryans brought with them a new language, a new pantheon of anthropomorphic gods, a patrilineal and patriarchal family system, and a new social order, built on the religious and philosophical rationales of varnashramadharma . Although precise translation into English is difficult, the concept varnashramadharma , the bedrock of Indian traditional social organization, is built on three fundamental notions: varna (originally, "color," but later taken to mean social class--see Glossary), ashrama (stages of life such as youth, family life, detachment from the material world, and renunciation), and dharma (duty, righteousness, or sacred cosmic law). The underlying belief is that present happiness and future salvation are contingent upon one's ethical or moral conduct; therefore, both society and individuals are expected to pursue a diverse but righteous path deemed appropriate for everyone based on one's birth, age, and station in life (see Caste and Class, ch. 5). The original three-tiered society--Brahman (priest; see Glossary), Kshatriya (warrior), and Vaishya (commoner)--eventually expanded into four in order to absorb the subjugated people--Shudra (servant)--or even five, when the outcaste peoples are considered (see Varna , Caste, and Other Divisions, ch. 5).
The basic unit of Aryan society was the extended and patriarchal family. A cluster of related families constituted a village, while several villages formed a tribal unit. Child marriage, as practiced in later eras, was uncommon, but the partners' involvement in the selection of a mate and dowry and bride-price were customary. The birth of a son was welcome because he could later tend the herds, bring honor in battle, offer sacrifices to the gods, and inherit property and pass on the family name. Monogamy was widely accepted although polygamy was not unknown, and even polyandry is mentioned in later writings. Ritual suicide of widows was expected at a husband's death, and this might have been the beginning of the practice known as sati in later centuries, when the widow actually burnt herself on her husband's funeral pyre.
Permanent settlements and agriculture led to trade and other occupational differentiation. As lands along the Ganga (or Ganges) were cleared, the river became a trade route, the numerous settlements on its banks acting as markets. Trade was restricted initially to local areas, and barter was an essential component of trade, cattle being the unit of value in large-scale transactions, which further limited the geographical reach of the trader. Custom was law, and kings and chief priests were the arbiters, perhaps advised by certain elders of the community. An Aryan raja, or king, was primarily a military leader, who took a share from the booty after successful cattle raids or battles. Although the rajas had managed to assert their authority, they scrupulously avoided conflicts with priests as a group, whose knowledge and austere religious life surpassed others in the community, and the rajas compromised their own interests with those of the priests.