Gingee Fort, about 100 km from Chennai, Tamil Nadu, is built on three hills – Krishnagiri, Chandragiri and Rajagiri – forming a triangle. The three together constitute a fort complex, each with a separate and self-contained citadel. The fort walls are 13 km (42,651 ft) long and the three hills are connected by walls enclosing an area of 11 sq. km. Built by the Chola dynasty in the 9th century CE, it was later modified during the Vijayanagar times.