Which empire built the road network centered on the Royal Road described by Herodotus?

The Achaemenid Empire built the Royal Road network described by Herodotus.

The Achaemenid, or First Persian, Empire created one of the ancient world’s most effective systems for moving officials, messages, armies, and goods. The best-known Royal Road connected Susa in southwestern Iran with Sardis in western Anatolia, a route of roughly 2,500 kilometers.

Greek historian Herodotus wrote that couriers used relay stations and fresh horses to carry royal messages quickly. His famous description emphasized that neither snow, rain, heat, nor darkness stopped the imperial postal service. The road was improved under Darius I, who ruled from 522 to 486 BCE.

The Royal Road was not a single modern-style paved highway throughout its length. It was a maintained route with stations, bridges, guards, and administrative support. Its infrastructure helped the empire govern a territory extending from the Indus Valley to southeastern Europe. Later rulers and civilizations continued using parts of the same transportation corridors.