I noted a couple of passages in this young-readers book. First (178), “And, as Christianity spread across the Roman world, Christian writers and teachers drew upon Seneca’s essays.” Second (199):
Unlike other fields of literature, in which the Roman imitated their Greek predecessors, letter writing was a uniquely Roman pursuit. For the Greeks, who traditionally lived in small communities and traveled only on occasion, the idea of writing to someone you might see that very day seemed pointless. By Pliny’s time, however, there was an extensive and well-maintained system of communication across the Roman empire. Mail traveled fairly rapidly, and it was the only way families and friends could stay in touch with those serving or living in distant provinces.
Letter writing among the Romans was, however, confined to the upper classes. The majority of Romans did not have the leisure time to write or the means to do so, for it was costly to send a letter. Furthermore, few ordinary citizens traveled far from their hometowns, so there was no reason for friends and relatives to write them letters. For the well-to-do, on the other hand, letter writing became the fashion, and Pliny developed it into an art form. Because of this, the scenes he describes generally concern the lives of those with influence and wealth, not the poor and uneducated.