Ymir. According to the Indo-European migration theory, the Indo-Iranians were the common ancestor of the Indo-Aryans and the Proto-Iranians. The Indo-Iranians split into the Indo-Aryans and Iranians around 1800-1600 BC. The Indo-Aryans were pastoralists who migrated into north-western India after the collapse of the Indus Valley Civilization, The Indo-Aryans were a branch of the Indo-Iranians, which originated in the Andronovo culture in the Bactria-Margiana era, in present northern Afghanistan. The roots of this culture go back further to the Sintashta culture, with funeral sacrifices which show close parallels to the sacrificial funeral rites of the Rigveda. Although some early depictions of deities seem to appear in the art of the Indus Valley Civilisation, very few religious artifacts from the period corresponding to the Indo-Aryan migration during the Vedic period remains. It has been suggested that the early Vedic religion focused exclusively on the worship of purely "elementary forces of nature by means of elaborate sacrifices", which did not lend themselves easily to anthropomorphological representations. Various artefacts may belong to the Copper Hoard culture (2nd millennium CE), some of them suggesting anthropomorphological characteristics. Interpretations vary as to the exact signification of these artifacts, or even the culture and the periodization to which they belonged. During the Early Vedic period (c. 1500 – 1100 BCE) Indo-Aryan tribes were pastoralists in north-west India. After 1100 BCE, with the introduction of iron, the Indo-Aryan tribes moved into the western Ganges Plain, adapting an agrarian lifestyle. Rudimentary state-forms appeared, of which the Kuru-tribe and realm was the most influential. It was a tribal union, which developed into the first recorded state-level society in South Asia around 1000 BCE. It decisively changed their religious heritage of the early Vedic period, collecting their ritual hymns into the Veda-collections, and developing new rituals which gained their position in Indian civilization as the orthodox Śrauta rituals, which contributed to the so-called "classical synthesis" or "Hindu synthesis". Rigvedic religion The Indo-Aryans brought with them their language and religion. The Indo-Aryan and Vedic beliefs and practices of the pre-classical era were closely related to the hypothesised Proto-Indo-European religion, and the Indo-Iranian religion. 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) Iran. 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.