As part of the Persian empire's expansion under Darius I, the Persians sought to strengthen trade with local economies rather than destroy them towards the general goal of economic prosperity. Within this new system, they developed official coinage and imposed a 20 percent tax for local populations. The Persians themselves paid no taxes, but 20 percent was a moderate rate for the time. This kept subjects of the Persian empire content enough not to revolt.
During Darius I's reign, the Persians also introduced agriculture and irrigation techniques into the areas in which they had expanded.Learn more about Mesopotamia