The evidence of written language is found across the Indus Valley. Stone seals and tablets, pottery, jewelry, and even copper weights all bear the same language. The problem is that no one has been able to crack the code and solve the mystery of this ancient language. It is clear that there was a uniform writing system across the Indus Valley, but until it is deciphered, it remains a constant mystery for historians studying the Indus River Valley. We have evidence of extensive trade with Mesopotamia which can help us to make sense of this civilization.