Maximian, residing in Milan, continues to govern…

Galerius, receiving Valeria, Diocletian's daughter, in marriage, resides in Sirmium; he is to watch over Illyria, the Danubian provinces, and Achaea.

Constantius Chlorus' Campaign Against Carausius and the Rise of Allectus (293 CE)

In 293 CE, Constantius Chlorus, newly appointed Caesar of the West under Emperor Diocletian’s Tetrarchy, was tasked with reclaiming Britain and northern Gaul from the usurper Marcus Aurelius Carausius. Carausius, a Menapian naval officer, had seized power in 286 CE, declaring himself Augustus and establishing an independent Britannic Empire.

1. The Fall of Gesoriacum (Bononia) and the Defeat of the Franks

• Constantius launched a campaign to isolate Carausius by attacking his mainland holdings.
• He successfully recaptured Gesoriacum (modern Boulogne, France), the key Roman naval base on the English Channel.
• To ensure a secure rear before invading Britain, he also defeated Carausius’ Frankish allies in Batavia, further cutting off continental support for the breakaway state.

2. The Assassination of Carausius and the Rise of Allectus

• The loss of Gaul and its ports weakened Carausius' position, reducing his ability to control trade and reinforce Britain.
• Sensing his vulnerability, his finance minister, Allectus, assassinated him in 293 CE and seized power.
• Allectus ruled Britain independently for three years, but his reign was not marked by open conflict with Rome, leading to a temporary period of peace.

3. Rome’s Next Move: Preparing for the Final Invasion

• Though the recapture of Bononia was a major victory, the Britannic Empire still controlled Britain and its defenses.
• Constantius could not immediately launch an invasion, as he needed time to build a new fleet and prepare a coordinated offensive.
• Over the next three years (293–296 CE), the Romans rebuilt their naval capabilities, setting the stage for the final reconquest of Britain in 296 CE.

4. Significance of the Conflict

• The fall of Gesoriacum marked the beginning of the end for the Britannic Empire, as it isolated Allectus’ regime from the continent.
• The assassination of Carausius demonstrated internal instability within the breakaway government.
• Although Allectus ruled peacefully for a time, he was ultimately unable to stop the Roman reconquest, which would come in 296 CE under Constantius Chlorus.

Conclusion: The Beginning of the End for the Britannic Empire

While Constantius’ victories on the continent weakened the secessionist state, the Britannic Empire under Allectus endured for three more years. However, Rome’s preparations for invasion were underway, ensuring that Britain would soon return to imperial control.

Constantius, assigned to Maximian and residing in Trier, takes charge of Gaul, Spain and Britain as Maximian has failed to suppress the revolts in Gaul and Britain.

Constantius had in 289 repudiated his wife (or concubine) Helena, mother of his son Constantine (the future emperor), in order to marry Maximian's stepdaughter Theodora.

Diocletian, having taken the title of “Augustus” and given it to his lieutenant Maximian as well, adds two more colleagues on March 1, 293: Galerius, a former herdsman born near Serdica, Thrace (now Sofia, Bulgaria), and Constantius Chlorus, a Dardanian nobleman according to the legend of his house, but a rather rude countryman also.

(Constantius's nickname Chlorus, meaning “The Pale,” is first found in Byzantine sources.)

These additional collaborators are each given the title “Caesar” and attached to an Augustus, Galerius to Diocletian himself.

Constantius’s son Constantine, born near Naissus probably in the later 280s, is brought up in the Eastern Empire at the court of Diocletian, who, residing in Nicomedia, watches over Thrace, Asia, and Egypt.

The empire now has four masters, celebrated by the authors of the Historia Augusta (the unreliable collection of biographies of Roman emperors and Caesars, published in the seventeenth century) as the quattuor principes mundi (“four princes of the world”).

Diocletian consecrates this human unity by forming a religious bond.

Because he believes that he has come to power through divine will, as revealed by the “fateful” boar, he regards himself and Maximian as “sons of gods and creators of gods.” In order to strengthen the union of the colleagues, each Augustus has formally adopted his Caesar.

The relationships are further cemented by marriage.

Thus, while the empire remains a patrimonium indivisum (”undivided inheritance”), it is nevertheless divided administratively.

Shapur’s grandson Bahram II had died in 293, and the enterprising Narseh, the youngest of Shapur’s sons passed over for the Sassanid succession and at that time viceroy of Armenia, had probably moved to eliminate Bahram III, a young man installed by a noble named Vahunam in the wake of his father’s death, and assumed the throne.

Narseh sends Diocletian the customary package of gifts in early 294, but within Persia he is destroying every trace of his immediate predecessors, erasing their names from public monuments.

He seeks to identify himself with the warlike reigns of Ardashir and Shapur, the same Shapur who had sacked Roman Antioch and reputedly skinned the captured Emperor Valerian to decorate his war temple.

Narseh is heir to Shapur's ambitions, and Persian opposition to the Romans extends from Egypt to Armenia.

Having incited uprisings by both the Blemmyes nomads in southern Egypt and the Arabs of the Syrian desert, and made use of anti-Roman propaganda by the Manichaeans and Jews, Narseh, taking advantage of the disarray in the Roman Empire, precipitates war in 295 or 296, apparently first invading the Roman protectorate of western Armenia, retaking the lands delivered to Tiridates in the peace of 287.

He will occupy the lands there until the following year.

Augusta Trevorum (present Trier) capital of the Roman province of Gallia Belgica, as well as the Roman prefecture of Gaul, from the second century, serves from about 295 as an imperial capital and residence.

Pannonia Inferior's southern and eastern districts are reorganized under Diocletian as Pannonia Secunda, which includes parts of present-day Serbia, Croatia, and Bosnia and Herzegovina, and Pannonia Valeria, which includes parts of present-day Hungary and Croatia.

Pannonia Superior is divided into Pannonia Prima and Pannonia Ripariensis (or Savia).

Galerius, as Diocletian’s caesar in the East, has fought hostile tribes along the Danube River for several years.

At the beginning of the Persian War in 296, Diocletian removes Galerius to the Euphrates to assume command of defensive operations against the Sassanians.

His first campaign ends in a crushing defeat, in the region between Carrhae (Harran, Turkey) and Callinicum (Ar-Raqqah, Syria), which causes the loss of Mesopotamia.

Diocletian may or may not have been present at the battle, but will present himself soon afterwards at …