Following his defeat of the Mughal emperor Humayun in 1541, Sher Shah Suri built a strong fortified complex at Rohtas, a strategic site in the north of what is now Pakistan. It was never taken by storm and has survived intact to the present day. The main fortifications consist of the massive walls, which extend for more than 4 km; they are lined with bastions and pierced by monumental gateways. Rohtas Fort, also called Qila Rohtas, is an exceptional example of early Muslim military architecture in Central and South Asia.