Literary canons have two intrinsically integrated yet distinct dimensions: they are simultaneously diachronic and synchronic. A canon is diachronic in its encyclopedic nature: it is based upon a selection of texts produced in the past that it organizes and preserves. It bears witness to a large body of past literature from which it selects its membership and without which it simply would not exist. Indeed, the canon is the artificially created image of a culture's past. A canon, however, is also synchronic because it is organizationally systematic in a normative sense: it consists of a controlled system of interrelated texts, the mutual relations of which (their hierarchies) are determined in the present. Ultimately, a canon witnesses the present order among texts that derive meaning from their relative placement within it. In every age, to join the canon means to intervene in and partake of both aspects. In the previous chapters, we have seen how Pliny's letters are involved in a process of constant cultural negotiation, how they propose a reinterpretation of the received past and seek to engage in the debates of the present. Chapter 2 examined Pliny's reworking of the Catullan heritage in light of what post-Augustan culture and society deemed appropriate literary behaviors. Chapters 3 and 4 highlighted several instances in which the letters became the privileged vehicle of Pliny's dialogue with Tacitus on the status of contemporary eloquence and the value of historiography.