The historian Polybius gives us a clear picture of the republican army at what is arguably its height in 160 BC. Serving in the army was part of Roman civic duty. To serve in the armies of Rome, one had to purchase one's own equipment, and soldiers were sorted into different classes according to wealth. Velites made up the lower class soldiers; it was this class which made up the majority of the heavy infantry legions characteristic to Rome. The Equites, or Equestrians, were the higher class citizens so named because they could afford to maintain at least one horse; this class made up the Roman Citizen Cavalry, which, through its evolution, transformed into one of the prizes of the late Republic, only to disappear by the time of the Empire.