ancient road running from Susa, the ancient capital of Persia, across Anatolia to the Aegean Sea, a distance of more than 1,500 miles (2,400 km). Royal messengers, who, according to the Greek historian Herodotus, were stopped by “neither snow, nor rain, nor heat, nor gloom of night,” traversed the entire road in nine days, thanks to a system of relays. Normal travel time was about three months. Alexander the Great made use of the Royal Road in his invasion and conquest of the Persian empire.