Bihar finds mention in the Vedas, Puranas, epics, etc., and was the main scene of activities of Buddha, and 24 Jain Tirthankars. Great rulers of the State before the Christian era were Bimbisar, Udayin, who founded the city of Pataliputra. Chandragupta Maurya and Emperor Ashoka and Maurya dynasty, the Sung and the Kanvas. Then came the Kushan rulers followed by Chandragupta Vikramaditya of the Gupta dynasty. Muslim rulers made in-roads into the territory during the medieval period. The first conqueror of Bihar was Mohammed- bin-Bakhtiar Khalji. The Tughluqs and then the Mughals followed the Khaljis. One of the major states of the Indian Union, Bihar is bounded on the north by Nepal, on the east by West Bengal, on the west by Uttar Pradesh and on the south by Jharkhand. Bihar has a number of rivers, the most important of which is the Ganga. The other rivers are the Sone, Poonpoon, Falgu, Karmanasa, Durgawati, Kosi, Gandak, Ghaghara, etc.