The Histories is a multi-volume work written by Polybius who was taken as a hostage to Rome after the Roman defeat of the Achaean League, and there he began to write an account of the rise of Rome to a world power. Polybius' Histories begin in the year 264 BC and end in 146 BC. He is primarily concerned with the 53 years in which Ancient Rome became a dominant world power. This period, from 220167 BC, saw Rome subjugate Carthage and gain control over Hellenistic Greece. Volume I of the Histories contains the first nine Books. Books I through V cover the affairs of important states at the time (Ptolemaic Egypt, Hellenistic Greece, Macedon) and deal extensively with the First and Second Punic Wars. In Book VI he describes the Roman Constitution and outlines the powers of the consuls, Senate and People. He concludes that the success of the Roman state was based on their mixed constitution, which combined elements of a democracy, aristocracy, and monarchy.

Polybius (c.200-c.118 BC) was a Greek historian of the Hellenistic period noted for his work The Histories, which covered the period of 264146 BC in detail. The work describes the rise of the Roman Republic to the status of dominance in the ancient Mediterranean world and includes his eyewitness account of the Sack of Carthage in 146 BC. Polybius is important for his analysis of the mixed constitution or the separation of powers in government, which was influential on Montesquieu's The Spirit of the Laws and the framers of the United States Constitution.