Anirudddha was Krishna's grandson and Usha, the daughter of an Asura king, therefore was no way any side would consent to their love.
Banasura was a great devotee of Shiva, and as a boon had asked him and his entire family to guard the gates of his city, Tezpur.
Both sides were nearly wiped out and a final battle followed between Shiva and Krishna; eventually, Brahma requested both of them to stop the war by putting him between them.
The stone sculptures on the Agnigarh hill portray this story of love and great war.
[2] Present day Agnigarh is a hill on the banks of the Brahmaputra which is one of the big tourist attractions in Tezpur.