historically dated to the second half of the second millennium BCE. Historically, after the collapse of the Indus Valley civilisation, which occurred around 1900 BCE, groups of Indo-Aryan peoples migrated into north-western India and started to inhabit the northern Indus Valley. The Indo-Aryans represented a sub-group that diverged from other Indo-Iranian tribes at the Andronovo horizon before the middle of the 2nd millennium BCE, The Indo-Iranians originated in the Sintashta culture, from which arose the subsequent Andronovo horizon. The Indo-Aryans migrated through the adjacent Bactria–Margiana area (present-day northern Afghanistan) to northwest India, followed by the rise of the Iranian Yaz culture at 1500 BCE, and the Iranian migrations into Iran at 800 BCE. Some Indian writers and archaeologists have opposed the notion of a migration of Indo-Aryans into India, and argued for an indigenous origin of the Indo-Aryans. In this view, "the Indian civilization must be viewed as an unbroken tradition that goes back to the earliest period of the Sindhu-Sarasvati (or Indus) tradition (7000 or 8000 BCE)." Though popular in India, and reflecting Indian views on Indian history and religion, the idea of a purely indigenous origin of the Indo-Aryans is outside the academic mainstream. The knowledge about the Aryans comes mostly from the Rigveda-samhita, i.e. the oldest layer of the Vedas, which was composed 1200–1000 BCE. They brought with them their distinctive religious traditions and practices. The Vedic beliefs and practices of the pre-classical era were closely related to the hypothesised Proto-Indo-European religion, and the Indo-Iranian religion. Funeral sacrifices from the Sintashta-culture show close parallels to the sacrificial funeral rites of the Rigveda, while, according to Anthony, the Old Indic religion probably emerged among Indo-European immigrants in the contact zone between the Zeravshan River (present-day Uzbekistan) and (present-day) Tajikistan. It was "a syncretic mixture of old Central Asian and new Indo-European elements", which borrowed "distinctive religious beliefs and practices" from the Bactria–Margiana culture, including the god Indra and the ritual drink Soma. Early Vedic period (c. 1500 BCE – c. 1000 BCE) The Rigveda contains accounts of conflicts between the Aryas and the Dasas and Dasyus. It describes Dasas and Dasyus as people who do not perform sacrifices (akratu) or obey the commandments of gods (avrata). Their speech is described as mridhra which could variously mean soft, uncouth, hostile, scornful or abusive. Other adjectives which describe their physical appearance are subject to many interpretations. However, some modern scholars