Europe 323: Licinius and the Goths
The Peace of Serdica held for several years, but in 323 Tervingi Goths crossed into Licinius’ territory and, when Licinius failed to oppose them, Constantine also entered Licinius’ territory and drove them back. Licinius immediately accused Constantine of violating the peace, while Constantine denounced Licinius for failing to protect the frontier, and war soon broke out among the two.
318 Licinius’ Sarmatian campaign▲
In 318 Licinius fought a small campaign against the Sarmatians. Little is known about this campaign, except that the Sarmatians seem to have been far from their traditional homeland. It is also around this time that the Carpi ceased to be a major tribal power, giving the Sarmatians and the Tervingi Goths a common border.
318–323 Crispus’ Germanic War▲
In 318, despite being only about 15, Constantine’s son Crispus was sent to Gaul to take up command there. Crispus waged at least two successful campaigns—against the Franks in 319 or 320 and against the Alemanni in 323—and thereby restored stability on the frontier. In 324 Crispus returned east with a force strengthened by Frankish auxiliaries to support his father against Licinius.
321 Constantine–Licinius rift▲
Following the Peace of Serdica in 317, Constantine and Licinius cooperated in the ruling of the Roman Empire for several years, but by 321 a permanent rift had formed between the two. In that year, rather than electing two consuls together, Constantine and Licinius each elected two separate consuls: Crispus and Constantine II in the West; and Licinius and Licinius II in the East. At the same time, at least according to Constantinian propaganda, Licinius initiated a new round of persecutions against the Christians, going against the 313 “Edict of Milan”.
In 322 the Sarmatians crossed the Danube in boats and laid siege to the town of Campona, setting its walls on fire. Constantine quickly arrived and put the invaders to flight, but soon afterwards the survivors—or possibly another party of Sarmatians—made another attack on the Roman Empire at Margum. Constantine won this encounter too and chased the Sarmatians across the Danube, where he killed their king Rausimod and seized vast numbers of captives.
In early 323, while Constantine was in Thessalonica supervising the construction of his fleet, a force of Tervingi Goths under their leader Getas crossed the Danube into Licinius’ territory and advanced through the provinces of Lower Moesia and Thrace in the west of the Diocese of Thraciae, causing destruction but encountering no resistance from Licinius’ troops. In late April Constantine cancelled all military leave and announced severe penalties for collaborating with the barbarians, then marched into Licinius’ territory to face them. Fear of Constantine apparently persuaded the Goths to hand over their loot and prisoners and return north, but the incident drew condemnation from Licinius, who claimed that Constantine, by crossing into his domain, had violated the Peace of Serdica. Whether or not Licinius himself had been conspiring with the Goths from the start has long been debated by historians, but he seems to have enjoyed friendly relations with the Tervingi since 315 and they would quickly ally with him against Constantine in 324.