Bhismaknagar is a small town in Indian state of Arunachal Pradesh. It is located near Roing in Lower Dibang Valley district.
It is located in Dibang Valley district and is a sacred heritage of the Idu Mishmis. It is a symbol of past glory and indicate the high standard of civilisation that once prevailed around Bhismaknagar. Bhismaknagar must have been a strong hold of the Chutiyas (12th-16th century) but the excavations has been throwing new light on its much earlier antiquities, which confirms the presence of an earlier Chutiya kingdom as stated in Assam chronicles(7th century). Bhismaknagar has been identified with Sadhayapuri (or Svadhayapuri), the political centre of the Chutiya Kingdom. It is also an important place of heritage for the Idu Mishmis.