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 "Rig Veda". 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 srauta rituals, which contributed to the so-called "classical synthesis" or "Hindu synthesis". 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. At least 383 non-Indo-European words were borrowed from this culture, including the god Indra and the ritual drink Soma. According to Anthony, The oldest inscriptions in Old Indic, the language of the "Rig Veda", are found not in northwestern India and Pakistan, but in northern Syria, the location of the Mitanni kingdom. The Mitanni kings took Old Indic throne names, and Old Indic technical terms were used for horse-riding and chariot-driving. The Old Indic term r'ta, meaning "cosmic order and truth", the central concept of the "Rig Veda", was also employed in the mitanni kingdom. And Old Indic gods, including Indra, were also known in the Mitanni kingdom. Their religion was further developed when they migrated into the Ganges Plain after c. 1100 BCE and became settled farmers, further syncretising with the native cultures of northern India.