What is "agnigarh"

Agnigarh (Pron:/ægɪˈgɑː/) is a hillock located in Tezpur, Assam, India. In Hindu mythology, it is the site of the fortress which was built by Banasura to keep his daughter Usha in isolation. The name itself is derived from the words ' Agni' (meaning fire) and 'garh' (meaning fortress or wall) in Sanskrit.