Polybius was an ancient Greek historian known for his work, "The Histories," which covers the rise of the Roman Republic and its expansion. He lived from around 200 to 118 BCE and emphasized the importance of understanding history through a systematic approach, focusing on political and military events. His writings are notable for their analysis of the Roman political system, particularly the concept of mixed government, which combines elements of monarchy, aristocracy, and democracy. Polybius believed that this balance contributed to Rome's stability and success, influencing later political thought and historical writing.