The work became a model for all later encyclopedias in the breadth of subject matter examined, the need to reference original authors, and a comprehensive index list of the contents. The work is dedicated to the emperor Titus, son of Pliny's close friend, the emperor Vespasian, in the first year of Titus' reign. It is the only work by Pliny to have survived, and the last that he published, lacking a final revision at his sudden and unexpected death in the AD 79 eruption of Vesuvius.