How did the Persian Empire use mounted messengers and posthouses?

The Persian Empire established an efficient communication network to govern its vast territories by utilizing a system of relays involving mounted messengers and posthouses.1

This infrastructure was centered around the Persian Royal Road, which spanned over 2,400 kilometers (1,500 miles) from Susa to the Aegean Sea. To ensure rapid transmission of information, the empire placed posthouses at convenient intervals along its roads. These stations allowed messengers to swap horses and riders, maintaining high speeds that would have been impossible for a single traveler.21

The effectiveness of this relay system was famously noted by the Greek historian Herodotus, who observed that royal messengers could traverse the entire length of the road in just nine days—a journey that took normal travelers approximately three months. By facilitating such swift communication, the Persian postal system became a vital tool for imperial administration and military coordination.21