Others may want to say more, but in the meantime you might find this old answer of mine interesting: https://www.reddit.com/r/AskHistorians/comments/bwc19i/what_would_writing_and_sending_a_letter_involve/epzfodn?utm_medium=android_app&utm_source=share&context=3

Part 1:

I will focus on addressing your question about the logistics of writing and delivering letters in the Roman world but I have to do so mainly in the period near and around the end of the Republic and be more focused around political and military letter dispatches. For a multiple-continent spanning empire, communication and up-to-date news was vital. The leading governing body, the Senate, was located at Rome and had delegated the administration of local areas of the empire to various Roman magistrates (proconsuls, propraetors, procurators, etc.), client-kings, or some kind of native ruling elite. The bureaucracy for the empire was large (hardly so by modern standards) because the Romans needed local control and organization to fill the gaps left by the technological limits of communication and the immense distances Roman control stretched over. Thus, writing letters, orders, and reports became massively important to the Senate so that they could stay updated on the administration of the empire, any wars currently being fought, provincial unrest or rebellion, how magistrates were operating, etc. We know that Roman commanders and magistrates sent reports back to the Senate in Rome and local officials and army commanders to their governors. Julius Caesar, whist fighting in Gaul in the 50s BCE, got plenty of written updates and/or descriptions from his legates and he reports numerous times about how he sent written reports back to Rome that covered his actions as governor. This is confirmed by Cicero but we do not know how detailed these reports were or what they looked like. We do know that the reports coming to him from his sub-commanders and those to the Senate later functioned as the basis for his Commentarii de Bello Gallico (Commentaries on the Gallic War)- a record of the campaigns he fought in Gaul but also a testimony of his achievements and triumphs over the dreaded Gallic foe. The time around the Gallic wars actually provides a great deal of information around how the Roman courier and messenger system worked because in this period we also have the surviving letters of Cicero, which includes some to his brother Quintus who was in Gaul fighting as one of Caesar’s legates (effectively an army commander/general). We get the impression from this period that there was plenty of information coming into Rome from which the Senate could judge the reports of Caesar, who at this time had many personal and political enemies in that body who wished to find fault in his activities and arrangements. Very little of these other documents and eyewitness evidence coming from Gaul survive but the volume of it must have been substantial. For example, from Cicero’s corpus of letters, we know he was in regular communications with his brother Quintus in Gaul. We know of one letter from 54 BCE (mentioned in Letters to Brother Quintus) that Caesar tells Cicero that he should not worry about his brother if he does not hear from him in a while since Quintus is with him fighting in Britain. What’s clear from this exchange is that Cicero expected to be in constant contact with his brother, which could only be done if there was a regular and working system of couriers and messengers; also factor in that this letter service was happening, in Roman terms, even at the very edge of the world. Naturally, information and news didn’t just flow into Rome and stop there, instead it came out of Rome and into the provinces and the empire at large. Again, evidence from this period highlights this when disparaging information of Caesar is circulating around his soldiers and officers- and among his enemies. Ariovistus, leader of the Suebi, in their meting recorded by Caesar, comments on Caesar's political opposition in Rome. Cassius Dio, writing much later, states that Caesar's soldiers were hearing news and ill opinions of him from back in Italy. What’s clear from our literary evidence is that a developed system of messengers operated in the Roman Empire, even in hostile territories and warzones.

Continue to Part 2.