A system of royal roads united the far-flung empire. To improve communication even further, the Persians set up a mail system to carry government documents. Government mail carriers sped along royal roads, dotted with rest stops supplied with fresh horses and new messengers.
Like Hammurabi, Darius adapted laws from the people he conquered and drew up a single code of laws for the empire. To encourage unity, he had hundreds of miles of roads built or repaired. Roads made it easier to communication with different parts of the empire. Darius himself kept moving from one capital to another. In each, he celebrated important festivals and was seen by the people.
To improve trade, Darius set up a common set of weights and measures to be used throughout the empire. He encouraged the use of coins, which the Lydians of Asia Minor had first introduced. Most people continued to be part of the barter economy, or the exchange of one set of goods or services for another. Coins, however, brought merchants and traders into an early form of a money economy. In a money economy, people pay for goods and services by exchanging tokens of an agreed value, such as coins. By minting his own gold coins, Darius hoped not only to project his power but also expand commerce and trade across his empire.
Nebuchadnezzar rebuilt Babylon. The Ishtar Gate to the city, a reconstruction of which is shown here, is famous for its blue bricks and depictions of various Babylonian gods.
Religious beliefs put forward by the Persian thinker Zoroaster (ZOH ruh as tur) also helped to unite the empire. Zoroaster lived about 600 B.C. He rejected the old Persian gods and taught that a single wise god, Ahura Mazda (AH hoo ruh MAHZ duh), ruled the world. Ahura Mazda, however, was in constant battle against Ahriman (AH rih mun), the prince of lies and evil. Each individual, said Zoroaster, had to choose which side to support.
Zoroastrian teachings were collected in a sacred book, the Zend-Avesta. According to Zoroaster, Ahura Mazda would triumph over the forces of evil. On a final judgment day, all individuals would be judged for their actions. Those who had done good would enter paradise. Evildoers would be condemned to eternal suffering.
Three other religions that emerged in the Middle East, Judaism, Christianity, and Islam, also stressed ideas of an individual's freedom to choose good or evil, and the latter two religions also included the concepts of heaven and hell, and a final judgment day.
These archers decorated the palace of Darius I, whose military campaigns expanded the Persian empire. Darius also encouraged cultural and artistic growth and developed judicial systems.
The Persian empire is often seen as one of the most important civilizations of the ancient world in part because of its influence on later people. The empire stretched across a huge area and brought diverse people under its control.