sources. As historian Polybius wrote several works, most of which are lost. His earliest work was a biography of the Greek statesman Philopoemen; this work was later used as a source by Plutarch when composing his Parallel Lives; however, the original Polybian text is lost. In addition, Polybius wrote an extensive treatise entitled Tactics, which may have detailed Roman and Greek military tactics. Small parts of this work may survive in his major Histories, but the work itself is lost, as well. Another missing work was a historical monograph on the events of the Numantine War. The largest Polybian work was, of course, his Histories, of which only the first five books survive entirely intact, along with a large portion of the sixth book and fragments of the rest. Along with Cato the Elder (234–149 BC), he can be considered one of the founding fathers of Roman historiography. Livy made reference to and uses Polybius' Histories as source material in his own narrative. Polybius was among the first historians to attempt to present history as a sequence of causes and effects, based upon a careful examination and criticism of tradition. He narrated his history based upon first-hand knowledge. The Histories capture the varied elements of the story of human behavior: nationalism, xenophobia, duplicitous politics, war, brutality, loyalty, valour, intelligence, reason and resourcefulness. Aside from the narrative of the historical events, Polybius also included three books of digressions. Book 34 was entirely devoted to questions of geography and included some trenchant criticisms of Eratosthenes, whom he accused of passing on popular preconceptions or laodogmatika. Book 12 was a disquisition on the writing of history, citing extensive passages of lost historians, such as Callisthenes and Theopompus. Most influential was Book 6, which describes Roman political, military, and moral institutions, which he considered key to Rome's success; it presented Rome as having a mixed constitution in which monarchical, aristocratic and popular elements existed in stable equilibrium. This enabled Rome to escape, for the time being, the cycle of eternal revolutions (anacyclosis). While Polybius was not the first to advance this view, his account provides the most cogent illustration of the ideal for later political theorists. A key theme of The Histories is the good statesman as virtuous and composed. The character of the Polybian statesman is exemplified in that of Philip II. His beliefs about Philip's character led Polybius to reject historian Theopompus'