Diogenes Laertius' Lives of Ancient Philosophers, covering the pre-Socratics to the Hellenistic period, is the most comprehensive surviving philosophical historical work from the Greek-Roman antiquity. It likely dates from the first half of the third century AD, during the peak of Roman jurisprudence and Greek philosophical commentary on Aristotle. The biographies of the 82 authors presented by Diogenes include information about their origins, lives, personalities, works, letters, wills, and circumstances of death, supplemented by anecdotes and quotes. They provide a good overview not only of the individual philosophical schools but also of the relationships that existed between them. Diogenes can be regarded as a "key witness" of ancient philosophy.