The very first people to establish a civilization in ancient India lived in the region known as the Indus River Valley.  There, they established the cities of Mohenjo-Daro and Harappa which flourished for over a thousand years.  With the arrival of the Aryans around 1500 B.C., India began to implement the caste system to separate members of society into different varanas.  HInduism and later Buddhism became the major religions of the region as tribes led by rajas replaced the great Indus River Valley Civilizations.  After invasions by the Persians and Alexander the Great, India's first empire was founded under Chandragupta Maurya who created the Mauryan Dynasty in 320 B.C.  This lasted until 183 B.C. and India would not be united again until the arrival of the Gupta Dynasty which lasted from 320 C.E. until 550 C.E.