The Indus River Valley civilization was one of the earliest urban societies in Asia, dating back 4500 years to the cities of Harappa and Mohenjo-Daro. It declined between 1700-1500 BCE after nearly a millennium of prosperity due to earthquakes and floods. Around 1500 BCE, nomadic Aryan groups settled in South Asia and developed Sanskrit. Over time, a caste system emerged organizing society into distinct social groups. The Mauryan Empire rose to power in the 300s BCE under the rule of Emperor Ashoka, who promoted Buddhism. The Gupta Empire in the 4th century AD was a period of cultural and scientific achievements. British rule from the mid-1800s onward led to