Necessity. Communication in the Roman empire was expensive, slow, unreliable, and yet, utterly crucial. Emperors, generals, soldiers, tax collectors, priests, businessmen, and women, and any other kind of traveler, had to send and receive information in order to function and survive. An accurate knowledge of events was necessary to preserve order at all levels of society: news of a military victory or failure would affect the subsequent decisions of an army on campaign; the yield of an individual's farm in an unpredictable season would affect his credit, either positively or negatively, in commercial transactions abroad; the political maneuvering of a provincial magnate would have to be reported with accuracy to his rival elsewhere; a matter of law that had been settled by the emperor would have to be made known to all residents of the empire. Written documents were needed to...