The Epistulae are a series of personal missives by Pliny the Younger directed to his friends and associates. These letters are a unique testimony of Roman administrative history and everyday life in the 1st century. The style is very different from that in the Panegyricus, and some commentators maintain that Pliny initiated a new genre: the letter written for publication. This genre offers a different type of record than the more usual history; one that dispenses with objectivity but is no less valuable for it. Especially noteworthy among the letters are two in which he describes the eruption of Mount Vesuvius in August 79 during which his uncle Pliny the Elder died (Epistulae VI.16, VI.20), and one in which he asks the Emperor for instructions regarding official policy concerning Christians (Epistulae X.96). The Epistulae are usually treated as two halves: those in Books 1 to 9, which Pliny prepared for publication, and those in Book 10, all of which were written to or by the Emperor Trajan during Pliny's governorship of Bithynia-Pontus. This final book was, significantly, not intended for publication. Other major literary figures of the late 1st century AD appear in the collection as friends or acquaintances of Pliny's, e. g. the poet Martial, the historian Tacitus and the biographer Suetonius. However, arguably the most famous literary figure to appear in Pliny's letters is his uncle. His nephew provides details of how his uncle worked tirelessly to finish his magnum opus, the Historia Naturalis (Natural History). Since Pliny the Younger was heir to his uncle's estate, he inherited his uncle's large library, and benefited from the acquisition.
As already mentioned above, highlights of these books include Pliny's description of the eruption of Mount Vesuvius and the death of his uncle and mentor, Pliny the Elder. The first letter (1.1), directed to Gaius Septicius Clarus, is also notable for giving Pliny's reasons for collecting his letters. Those that give details of Pliny's life at his country villas are important documents in the history of garden design. They are the world's oldest sources of the information on how gardens were used in the ancient world and the considerations that went into their design.