Constantius and his praetorian prefect, Asclepiodotus, launch…

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 …

…Antioch, where the official version of events is made clear: Galerius is to take all the blame for the affair.

In Antioch, Diocletian forces Galerius to walk a mile in advance of his imperial cart while still clad in the purple robes of an emperor.

The message conveyed is clear: the loss at Carrhae is not due to the failings of the empire's soldiers, but due to the failings of their commander, and Galerius' failures will not be accepted.

(It is also possible that Galerius' position at the head of the caravan is merely the conventional organization of an imperial progression, designed to show a Caesar's deference to his Augustus.)

The Scots raid Great Britain from Ireland in the west.

The name “Picts” first appears in Roman sources in 296 in reference to all the northern tribes that raid Roman Britannica.

A people of obscure origin, these ancient inhabitants of northern Scotland apparently speak a form of “p”-Celtic related to Welsh but incorporating pre-Celtic elements.

A group of Roman troops, who had been separated from the main body by the fog during the channel crossing, sails up the Thames to catch up with the remnants of Allectus's men, mostly Franks, at Londinium (London), and massacres them.

Constantius himself, it seems, does not reach Britain until it is all over (his panegyrist claims he was welcomed by the Britons as a liberator).

He now sets about restoring frontier defenses.

Lucius Domitius Domitianus revolts against Diocletian in 297, seizing power for a short time in Aegyptus province, but dies in December of the same year, when Diocletian goes to Aegyptus to quell with the revolt.

Numismatic and papyrological evidence support Domitianus' claim for the purple.

It is possible that the rebellion had been sparked by a new tax edict, but this uncertain.

Galerius is reinforced, probably in the spring of 298, by a new contingent collected from the empire's Danubian holdings.

Narseh does not advance from Armenia and Mesopotamia, leaving Galerius to lead the offensive in 298 with an attack on northern Mesopotamia via the mountains of Armenia.

Diocletian may or may not have been present to assist the campaign.

Narseh retreats to Armenia to fight Galerius' force, to Narseh's disadvantage: the rugged Armenian terrain is favorable to Roman infantry, but unfavorable to Sassanid cavalry.

Local aid gives Galerius the advantage of surprise over the Persian forces, and, in two successive battles somewhere near the Upper Tigris River, Galerius annihilates a much superior Persian force.

During the second encounter, Galerius captures a great deal of plunder, along with King Narseh’s harem and family.

Following up his advantage, he takes the city of Ctesiphon.

Narseh's wife is to live out the remainder of the war in Daphne, a suburb of Antioch, serving to the Persians as a constant reminder of Roman victory.

Galerius advances into Media and Adiabene, winning continuous victories, most prominently near Erzurum, and …

…securing Nisibis (Nusaybin, Turkey) before October 1, 298.

Narseh sues for peace and Galerius compels the Persian monarch to accept Roman terms.

The resultant peace of Nisibis reinstates a Roman protégé in Armenia and gives the empire a part of Upper Mesopotamia that extends to five provinces northeast of the Tigris, which marks the greatest extension of the Roman Empire in the east.

The Persians also recognize the newly installed Roman puppet king of Armenia, Tiridates III; The Romans, for their part, return Narseh’s captive family and concubines.

Peace is thus assured for some decades.

By this treaty, which will last for forty years, the Sassanians withdraw completely from the disputed districts.