Diogenes Laërtius, who lived in the third century AD, wrote Lives and Opinions of Eminent Philosophers, a voluminous collection of biographies of nearly every Greek philosopher who ever lived. Unfortunately, Diogenes Laërtius often fails to cite his sources and many modern historians consider his testimony unreliable. Nonetheless, in spite of this, he remains the only available source on the lives of many early Greek philosophers."Diogenes Laërtius", The Columbia Electronic Encyclopedia, 2013 His book is not entirely without merit; it does preserve a tremendous wealth of information that otherwise would not have been preserved. His biography of Epicurus, for instance, is of particularly high quality and contains three lengthy letters attributed to Epicurus himself, at least two of which are generally agreed to be authentic.
