Sestertius

A major Roman coin

The sestertius was one of the main denominations of the Roman monetary system, used over a long period during the Republic and, especially, the Empire. Its name comes from the Latin expression semis tertius, meaning ‘two and a half’, a reference to its original value.

Originally, the sestertius was worth a quarter of a denarius, or 2½ asses. When the denarius was revalued at sixteen asses, the sestertius became worth four asses, while remaining a quarter denarius. This was also its value in the Augustan system.

From a small silver coin to a large brass denomination

The earliest sestertius was a small silver coin. Under Augustus’ monetary reform it became a large coin made of orichalcum, a copper-zinc alloy (brass), recognisable by its broad diameter and substantial weight.

Sestertius, obverse	Sestertius, reverse

This transformation made the sestertius one of the most characteristic coins of the Roman Empire, often depicting emperors, deities and commemorative scenes.

Economic role

The sestertius was widely used to express prices, wages and accounting entries. Large sums were often stated in sestertii even when other coins were used in the actual transaction.

It therefore also served as a unit of account, a function later performed in medieval systems by the pound and the shilling.

Relationship with the denarius

The sestertius was closely related to the denarius, a central denomination of the Roman monetary system. In the classical accounting system, four sestertii equalled one denarius; this relationship should be distinguished from changes in the coins’ metal content.

As the imperial monetary system changed and the metal content of its coinage declined, the role of the sestertius also changed, and the denomination eventually disappeared.