The Bhismaknagar Fort is a major sightseeing point in Arunachal Pradesh. The fort was built in the 8th century BC. It is the oldest of all the archaeological sites constructed in the area. This fort in the Dibang Valley district is regarded sacred by the Idu Mishims. It symbolizes the glory of the past. Built with clay bricks and adorned with pottery, the fort was constructed in the 4th century.