the nephew of the late Kuru king). According to post-Vedic Sanskrit literature, the capital of the Kurus was later transferred to Kaushambi, in the lower Doab, after Hastinapur was destroyed by floods as well as because of upheavals in the Kuru family itself. In the post Vedic period (by the 6th century BCE), the Kuru dynasty evolved into Kuru and Vatsa janapadas, ruling over Upper Doab/Delhi/Haryana and lower Doab, respectively. The Vatsa branch of the Kuru dynasty further divided into branches at Kaushambi and at Mathura. According to Buddhist sources, by the late and post-Vedic periods, Kuru had become a minor state ruled by a chieftain called Koravya and belonging to the () . After the main Kuru ruling dynasty had moved to Kosambi, the Kuru country itself became divided into multiple small principalities, with the ones at Indapatta and one at Iṣukāra being the most prominent ones. By the time of the Buddha, these small statelets had been replaced by a Kuru (republican state). Society The tribes that consolidated into the Kuru Kingdom or 'Kuru Pradesh' were largely semi-nomadic, pastoral tribes. However, as settlement shifted into the western Ganges Plain, settled farming of rice and barley became more important. Vedic literature of this time period indicates the growth of surplus production and the emergence of specialized artisans and craftsmen. Iron was first mentioned as śyāma āyasa (श्याम आयस, literally "black metal") in the Atharvaveda, a text of this era. Another important development was the fourfold varna (class) system, which replaced the twofold system of arya and dasa from the Rigvedic times. The Brahmin priesthood and Kshatriya aristocracy, who dominated the arya commoners (now called vaishyas) and the dasa labourers (now called shudras), were designated as separate classes. Kuru kings ruled with the assistance of a rudimentary administration, including purohita (priest), village headman, army chief, food distributor, emissary, herald and spies. They extracted mandatory tribute (bali) from their population of commoners as well as from weaker neighboring tribes. They led frequent raids and conquests against their neighbors, especially to the east and south. To aid in governing, the kings and their Brahmin priests arranged Vedic hymns into collections and developed a new set of rituals (the now orthodox Srauta rituals) to uphold social order and strengthen the class hierarchy. High-ranking nobles could perform very elaborate sacrifices, and many poojas (rituals) primarily exalted the status of the king over his people.