The earliest society in South Asia was the Harappan civilization (ca. 2500–2000 B.C.E.) based in the Indus River Valley. They left written records, but their script remains undeciphered. With the Harappans’ decline, a group who called themselves Aryans came to dominate North India. Around 1500 B.C.E., the Aryans began to compose oral poetry in Sanskrit, an Indo-European language closely related to ancient Persian and Hittite. According to the Rig Veda (see Document 1-1), the earliest record of this sacred poetry, the Aryan religion initially focused on ritual sacrifices conducted by the priestly caste (Brahmins), who sought material benefits. Later religious movements in India, such as Buddhism, instead sought to fill spiritual needs and ignored the Aryans’ strict caste system. In reaction to Buddhism, the Brahmins rejected ritual sacrifices and helped spread the worship of gods, such as Krishna, to all levels of society.