Also in northern India, the agriculture that arose in the Indus River led to the formation of states over 1,500 years. Howeve, only in 400 B.C. a warrior named Chandragupta unified the entire subcontinent under the Maurian Empire. India was consolidated as a society of castes, with a rich religious philosophy, written on the Vedas and, from fifth century b.C., with Buddhism. Buddhism developed from the teachings of its founder, Siddhartha Gautama, known as the Buddha, and expanded rapidly. In the third century B.C., Emperor Asoka made it the official religion of his vast empire and sent embassies of Buddhist monks throughout the then-known world.