Wikipedia
Banaili estate in Bihar was one of the largest estates in India. It covered parts of regions that are currently located in four of India's current states, namely, Bihar, Jharkhand, West Bengal and Orissa.
The name of the estate derives from a village Banaili 1 in the then Purnia district of Bihar.
The main centres of residences of Rajas of Banaili are Banaili, Ramnagar, Champanagar, Srinagar, Garh Banaili, and Sultanganj. Bhagalpur was the centre from where administration of the estate was carried out.
One of the centres of Banaili Raj located in Sultanganj is believed to have ancient historical or mythical association. The Krishnagarh palace built by Kumar Krishnanand Singh on Sultanganj is in the Karnagarh area, which is believed to be place where the Castle of King Karna of Mahabharata was located.2