Polybius of Megalopolis (c. 200–c. 118 BCE) was a Greek statesman and historian of the Hellenistic period. Born into the political elite of the Achaean League, he was taken to Rome as a hostage in 168 BCE and detained for seventeen years [1][2]. There, he formed a close association with Scipio Aemilianus, gaining direct access to Roman military and political circles, which he later used to aid in the settlement of Greece after 146 BCE [1][2].

His major work is The Histories (Ἱστορίαι), a 40-book universal history of Rome's rise from 264 to 146 BCE, of which only Books 1–5 survive complete [1][2][3]. Other, now lost, works included a Life of Philopoemen, a treatise on Tactics (Τακτικά), a History of the Numantine War, and a geographical work On the Habitability of the Equatorial Region [1].

Polybius is a historian of paramount importance, providing the principal surviving narrative for Rome's expansion. He championed a rigorous, "pragmatic" methodology and offered a unique bicultural analysis, most famously in his influential theory of the Roman mixed constitution as the source of its political strength [1][2][3].

Sources 1. Stanford Encyclopedia of Philosophy (Plato.stanford.edu): https://plato.stanford.edu/entries/polybius/ 2. Encyclopædia Britannica: https://www.britannica.com/biography/Polybius 3. Perseus Digital Library (Tufts University): http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.01.0234