NBC3740 A clay tablet recording a contract was often encased in a clay envelope which was not broken until the contract was fulfilled. The breaking of the envelope can be compared to the modern practice of burning the mortgage. It symbolizes the termination of an obligation. An important aspect of economic life is international trade. The fact that it involves at least two jurisdictions considerably increases the likelihood that prices are flexible and open to free markets. International trade flourished to the North in Anatolia, to the South into the Persian Gulf and possibly as far east as the Indus Valley civilization. This letter in the Old Assyrian dialect of Akkadian gives instructions regarding datum tax.