system, as Suetonius notes, because a courier who travels the whole distance could be interrogated by the emperor, upon arrival, to receive additional information orally. That may have had the additional advantage of adding security to the post, as one man had the responsibility to answer for the successful delivery of the message. That does not come without a cost, as the Romans could not relay a message as quickly as they could if it passed from one rider to the next. The cursus publicus was run by municipal magistrates until the reign of Nerva, who reformed the systems so it would be run by the Res mancipi. Many Roman roads were constructed or expanded the facilitate the movement of the cursus publicus. After the fall of the Roman Empire the Cursus Publicus survived in the Byzantine Empire and the former territories of the Western Roman Empire. Under the Byzantine Empire the agentes in rebus supervised the cursus publicus and ensured they had the necessary supplies and lodgings. They were also tasked with ensuring the legal validity of the diplomas their users possessed. Speed of post Procopius provides one of the few direct descriptions of the Roman post that allows an estimation the average rate of travel overland. In the 6th century, he described earlier times: If the distance between change stations is known, and five to eight is the average number, the speed of the cursus publicus can be calculated. A. M. Ramsey writes, "It appears from the Jerusalem Itinerary that the mansiones, or night quarters on the roads, were about twenty-five [Roman] miles [] apart, and, as Friedlander points out, the distance between Bethlehem and Alexandria (about 400 Roman miles []) was reckoned to be sixteen mansiones, that between Edessa and Jerusalem (by Antioch nearly 625 [Roman] miles []) twenty-five mansiones. Although no Itinerary gives a complete list of mutationes and mansiones for any road, the general rule seems to have been two mutationes between each two mansiones or 37 km (23 miles). This would make the 'stage' about eight and a third Roman miles []." The typical trip was per day or 5 to 8 stages. But this is in normal, not emergency, conditions, when a single rider could cover 160 km (100 miles) or more in a day There are several cases in which urgent news or eager officials traveled at a faster rate. There is