Have some information on ways of carrying messages quickly over long distances with limited tech

According to Herodotus, the distance [from Sardis to Susa on Darius the Great's Royal Road] could be covered in less than fifteen days, when the system of post horses was used. The road was divided into sections that could be covered in a day by a man on horseback. At each station, a rider would hand off his dispatch to a fresh rider and horse: "No mortal thing travels faster than these Persian couriers," Herodotus writes. ...

The Persian relay system appears to have been faster than any other until the thirteenth century, when Genghis Khan's couriers carried messages from his headquarters near the Yellow River in China to the western side of the Black Sea, a distance of more than 8,000 kilometres (5,000 miles.) Khan's system was somewhat different from the Persian one: each of the great Mongol leader's riders was responsible for the message he carried, and so one courier travelled the whole distance, strapping himself to his mounts so he would not fall off. (At the same time on the other side of the world, it should be noted, the Incas who did not have fast, load-bearing animals, were using fleet human runners to carry messages, as well as perishable items like fish, hundreds of kilometres in the Andes and its foothills.)

-- Mary Soderstrom, Road Through Time: The Story of Humanity on the Move