Agra Fort is a UNESCO World Heritage site located in Agra, India. The fort is also known as Lal Qila and Red Fort of Agra. It is about 2.5 km northwest of its much more famous sister monument, the Taj Mahal. This powerful fortress of red sandstone encompasses, within its 2.5-km-long enclosure walls, the imperial city of the Mughal rulers. Its construction along the bank of the Yamuna River was begun by Emperor Akbar in 1565. Further additions were made, particularly by his grandson Shah Jahan, using his favourite building material – white marble. The fort was built primarily as a military structure, but Shah Jahan transformed it into a palace, and later it became his gilded prison for eight years after his son Aurangzeb seized power in 1658. It is comprised of many fairy-tale palaces, such as the Jahangir Palace and the Khas Mahal; audience halls, such as the Diwan-i-Khas; and two very beautiful mosques.