The Chola dynasty was a Tamil thalassocratic empire of southern India and one of the longest-ruling dynasties in the world history. The earliest datable references to the Chola are from inscriptions dated to the 3rd century BCE during the reign of Ashoka of the Maurya Empire. As one of the Three Crowned Kings of Tamilakam, along with the Chera and Pandya, the dynasty continued to govern over varying territories until the 13th century CE. The Chola Empire was at its peak and achieved imperialism under the Medieval Cholas in the mid-9th century CE. The heartland of the Cholas was the fertile valley of the Kaveri River. 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. They unified peninsular India south of the Tungabhadra River, and held the territory as one state for three centuries between 907 and 1215 CE. Under Rajaraja I and his successors Rajendra I, Rajadhiraja I, Rajendra II, Virarajendra, and Kulothunga Chola I, the dynasty became a military, economic and cultural powerhouse in South Asia and Southeast Asia. The power and the prestige the Cholas had among political powers in South, Southeast, and East Asia at its peak is evident through their expeditions to the Ganges, naval raids on cities of the Srivijaya empire based on the island of Sumatra, and their repeated embassies to China. The Chola fleet represented the zenith of ancient Indian maritime capacity. During the period of 1010–1153 CE, the Chola territories stretched from the Maldives in the south to the banks of the Godavari River in Andhra Pradesh as the northern limit. Rajaraja Chola conquered peninsular South India, annexed part of the Rajarata kingdom in present-day Sri Lanka, and occupied Maldives islands. His son Rajendra Chola further expanded the Cholar territory by sending a victorious expedition to North India that touched the river Ganges and defeating the Pala ruler of Pataliputra, Mahipala. By 1019, he also completely conquered the Rajarata kingdom of Sri Lanka and annexed it to the Chola empire. In 1017 and 1025, Rajendra Chola launched raids on the cities of the Srivijaya empire. However, this invasion failed to install direct administration over Srivijaya, as the invasion was short and only meant to plunder the wealth of Srivijaya. However, the Chola influence on Srivijava would last until 1070, when the Cholas began