Though one of the oldest biography sources in Greco-Roman history, Plutarch's Parallel Lives is not a highly valued source of historical information. He does chronicle effective descriptions of the 48 men in question, but Plutarch's sources have long since been discredited on many accounts. He does, however, include several details which have informed the historical community about figures like Alexander the Great and Numa Pompilius.
As a concept, Plutarch comments that he approached this collection of biographies as a study of moral character and its consequences on reputation. He explores 48 famous historical figures, mostly politicians, soldiers, and other public figures. In correspondence with the title, Plutarch divides his subjects into pairs -- one Greek and one Roman -- in order to compare their lives. After each pair he analyzes the couple and the sometimes astonishing similarity or diversion of their stories. It's a bizarre look at the twists and turns of fate in relation to individual choices.
