In the Bibliotheca historica, Diodorus sets out to write a universal history, covering the entire world and all periods of time. Each book opens with a table of its contents and a preface discussing the relevance of history, issues in the writing of history or the significance of the events discussed in that book. These are now generally agreed to be entirely Diodorus' own work.[1] The degree to which the text that follows is derived from earlier historical works is debated.