Portrayal of Tetrarchic rule in the Roman Empire

For much of its history, the Roman Empire was effectively ruled by just one man (side note: There are several short periods when the Empire was temporarily ruled by two emperors, e.g. Marcus Aurelius and Lucius Verus in 161–169 CE.). This all changed when emperor Diocletian (284–305 CE) not only decided to split the Empire – which had grown unwieldy – into two administrative halves, but also appointed two emperors to each half: an Augustus (senior emperor) and a Caesar (junior emperor and successor).

This governmental system, with an imperial college consisting of four members, would later become to be known as the Tetrarchy. Although the system only lasted a few decades (side note: Diocletian lived long enough to see the collapse of his Tetrarchic system.), it’s had a lasting impact on the Empire and the artefacts it created.

Through analysis of coinage, monuments, speeches, inscriptions, and other written works, it is possible to reconstruct how the imperial college presented such a radical new governmental system to the people of the Empire in an age with low literacy rates and no mass media. Three main findings emerged from this analysis.

With a new governmental system in place that involves four rulers instead of just one, one would expect to find many monuments and artefacts that depict the four Tetrarchic rulers.

This is true to some extent: Imperial edicts, like the price edict and other legal standards for the Empire, name all four Tetrarchic rulers with their full titles. Inscriptions on milestones and some monuments also present the Tetrarchs as a collegium, for example, through direct portrayal of the four rulers, by addressing them together as DDDD(omini) NNNN(ostri), or by using metaphors (e.g. “four elements”, “four seasons”, “four lights of the world”).

However, we don’t see depictions of the entire group as often as we would expect.

Officially the Empire is ruled by the collegium as a whole, but the Tetrarchy is not necessarily a system with four equal emperors. For instance, depictions of the first collegium show that there is a strict hierarchical order that begins with the two Augusti, Diocletian and Maximian, followed by the two Caesares, Constantius and Galerius.

The Augusti are often featured more prominently than the two Caesares. In other cases, Diocletian is primarily depicted with greater prominence compared to other members of the collegium. Alternatively, depictions might present the two emperors of the western half (Maximian and Constantius) and those of the eastern part of the Empire (Diocletian and Galerius) separately.

In other words: the rule of four emperors is presented not as a single entity, but as a combination of two pairs of men. This implies precedence and likely helped legitimise the Tetrarchy, as the concept of shared power by two men was well-known within Roman society (side note: Some other prominent examples include of course Rome’s founders, Romulus and Remus, and the period of the Republic, during which two consuls were appointed every year to lead the city.).

Although the four rulers were collectively responsible for administration of the Empire, they rarely met. Each focussed on their own part of the Empire, which meant that in practice Roman citizens were mainly confronted with one ruler.

Therefore, artists would often focus their work on a single ruler while simultaneously emphasising their membership in the collegium. For example, the Arch of Galerius in Thessaloniki commemorates Galerius’s military victories. The Arch also features Diocletian in a supporting role, despite not having participated in the military campaign of his Caesar. His presence should largely be seen as symbolic – a means to convey the idea of a shared victory.