Stone Age tools found in Bangladesh indicate human habitation for over 20,000 years, and remnants of Copper Age settlements date back 4,000 years. Ancient Bengal was settled by Austroasiatics, Tibeto-Burmans, Dravidians and Indo-Aryans in consecutive waves of migration. Archaeological evidence confirms that by the second millennium BCE, rice-cultivating communities inhabited the region. By the 11th century people lived in systemically-aligned housing, buried their dead, and manufactured copper ornaments and black and red pottery. The Ganges, Brahmaputra and Meghna rivers were natural arteries for communication and transportation, and estuaries on the Bay of Bengal permitted maritime trade. The early Iron Age saw the development of metal weaponry, coinage, agriculture and irrigation. Major urban settlements formed during the late Iron Age, in the mid-first millennium BCE, when the Northern Black Polished Ware culture developed. In 1879, Alexander Cunningham identified Mahasthangarh as the capital of the Pundra Kingdom mentioned in the ''Rigveda''. The oldest inscription in Bangladesh was found in Mahasthangarh and dates from the 3rd century BCE. It is written in the Brahmi script.