How was the economy controlled in mesopotamia?

In Mesoptomia there may not have been money to buy and sell with, but there was a lot of buying and selling done by trading (i.e. the barter system) and assisted by the development of a writing system.   Writing's main purpose was to keep track of debit and credit accounts for merchants.  The function of a scribe was similar to that of an account; just balancing the amounts owed to one party by another.  Writing later became useful for many other reasons, but writing's economic use caused its invention!  Once a contract was done between two parties a cyclinder wheel sealed the deal.