The heartland of the Cholas was the fertile valley of the Kaveri River, but they ruled a significantly larger area at the height of their power from the later half of the 9th century till the beginning of the 13th century. The whole country south of the Tungabhadra was united and held as one state for a period of three centuries and more between 907 and 1215 AD. Under Rajaraja Chola I and his successors Rajendra Chola I, Rajadhiraja Chola, Virarajendra Chola, and Kulothunga Chola I, the dynasty became a military, economic and cultural power in South Asia and South-East Asia. The power of the new empire was proclaimed to the eastern world by the expedition to the Ganges which Rajendra Chola I undertook and by naval raids on cities of the city-state of Srivijaya, as well as by the repeated embassies to China. The Chola fleet represented the zenith of ancient Indian sea power.