In the Roman social hierarchy, the equestrian order stood second only to the senatorial aristocracy in status and prestige. Throughout more than a thousand years of Roman history, equestrians played prominent roles in the Roman government, army, and society as cavalrymen, officers, businessmen, tax collectors, jurors, administrators, and writers. This book offers the first comprehensive history of the equestrian order, covering the period from the eighth century BC to the fifth century AD. It examines how Rome's cavalry became the equestrian order during the Republican period, before analysing how imperial rule transformed the role of equestrians in government. Using literary and documentary evidence, the book demonstrates the vital social function which the equestrian order filled in the Roman world, and how this was shaped by the transformation of the Roman state itself.