A lost work is a document, literary work, or piece of multimedia produced some time in the past of which no surviving copies are known to exist. In contrast, surviving copies of old or ancient works may be referred to as extant. Works may be lost to history either through the destruction of the original manuscript, or through the loss of all later copies of a work. The term most commonly applies to works from the classical world, although it is increasingly used in relation to more modern works.
Works or fragments may survive, either found by archaeologists, or accidentally by anyone, as in the case of the spectacular find of the Nag Hammadi library scrolls. Works also survived when they were reused as bookbinding materials; when they were quoted or included in other works; or as palimpsests, which are documents made of materials that originally had one work written on them, but which were then cleaned and reused. The discovery in 1822 of large parts of Cicero's De re publica was one of the first major recoveries of an ancient text from a palimpsest, while another famous example is the discovery of the Archimedes palimpsest, which had been used to make a prayer book almost 300 years later. Works may be recovered in libraries as a lost or mislabeled codex, a palimpsest, or even as a part of another book or codex.
Most known missing works are described by works or compilations that survive, such as the Naturalis Historia of Pliny the Elder or the De Architectura by Vitruvius. Sometimes authors destroyed their own works. Other times they instructed others to destroy the work after their deaths; such action was not taken in several well-known cases, such as that of Virgil's Aeneid, which was saved by Augustus, and Kafka's novels, which were saved by Max Brod. Handwritten manuscripts existed in very limited copies before the era of printing, so the destruction of ancient libraries, including the multiple attempts on Alexandria, resulted in the loss of numerous works. Of course works that no one has subsequently referred to remain unknown.