How did Darius I standardize coinage, weights, and measures?

Darius I standardized coinage, weights, and measures as part of a broader administrative program to promote imperial trade and commerce throughout the Achaemenid Empire.123

His efforts included the following:

• Coinage: Darius was likely the first Achaemenid ruler to strike coins. He introduced the daric, a gold coin of high purity, and the siglos, a silver coin. The daric weighed 8.4 grams, and 20 silver sigloi were valued as equal to one gold daric. These coins featured a consistent design—the Persian king in a kneeling position holding a bow and spear—and were minted under the royal prerogative.4
• Weights and Measures: To facilitate public and private trade, Darius implemented imperial standards for weights and measures across his diverse provinces. This unification helped streamline economic activity and tax collection, as the empire moved toward a more organized fiscal structure.23

These reforms, alongside the development of an extensive road system and maritime routes, were intended to integrate the empire's economy and encourage commercial growth.23