The Indus Valley civilization arose around 3000 BCE along the Indus River valley in what is now Pakistan. At its height around 2500 BCE, the civilization was home to large urban centers like Harappa and Mohenjo-Daro with advanced infrastructure like sewage systems. Though the writing of the Indus Valley people remains undeciphered, they appear to have had a strong central government and engaged in extensive trade with Mesopotamia and other regions. By 1500 BCE, some Indus sites showed signs of decline possibly due to invasions by Aryan groups.