There exists a strong link in modern thinking between letter collections and biographical or historical narration. Many ancient letter collections have been rearranged by modern editors along chronological lines, apparently with the aim of realizing the biographical and historiographical potential of these ancient collections. In their original format, however, non-fictional Greco-Roman letter collections were arranged predominantly by addressee or by theme (often without the preservation of chronology within addressee or thematic groupings), or they might be arranged on the principle of artful variety and significant juxtaposition. Consequently, some purpose or purposes other than biographical or historical narration must be attributed to ancient letter collections. This paper asks what those purposes might be.