Answer:
Use of standardized metal coins.
Explanation:
According to a different source, these are the options that are included with this question:
- Use of standardized metal coins.
- Division of the empire into administrative provinces.
- Creation of a universal code of laws.
- Construction of the remarkable gardens of the palace in Babylon.
The use of standardized metal coins was the main innovation that allowed the Persian Empire to become more unified. As many people shared such coins, they began to see themselves as members of the same society. Moreover, these coins allowed trade to expand and become more efficient.
