A Roman civil war battle that ended in a stalemate and a fragile peace
The Battle of Mardia was a brutal, indecisive clash between emperors Constantine I and Licinius. Despite Constantine’s tactical maneuvers, the conflict concluded with neither side achieving a total victory. This stalemate eventually forced both leaders to the negotiating table, resulting in a temporary peace that reshaped the Roman government.
Fought in late 316 or early 317, the Battle of Mardia occurred after Constantine invaded the Balkan territories held by Licinius. This followed an earlier, crushing defeat for Licinius at Cibalae in October 316. Seeking to regain his footing, Licinius retreated to Adrianople, where he assembled a fresh army and elevated an officer named Valerius Valens to the rank of augustus. Constantine, insulted by this promotion, rejected subsequent peace overtures and marched his forces through the Balkan mountains to engage his rival.
The engagement itself was fierce and inconclusive. As night fell, the fighting paused, but Constantine attempted to break the deadlock by sending a detachment to strike Licinius from the rear. While this forced Licinius to pull back, his troops maintained their discipline and withdrew in good order. Both armies suffered significant casualties during the struggle. Under the cover of darkness, Licinius successfully prevented his forces from collapsing and retreated toward Beroe, leaving Constantine victorious in the field but unable to secure a decisive end to the war.
The aftermath saw Constantine miscalculate, believing Licinius was fleeing toward Byzantium. This error placed Constantine in a vulnerable position, effectively cutting him off from his own supply lines. Recognizing the precariousness of their respective situations, both emperors eventually sought a settlement. The resulting peace, finalized at Serdica on March 1, 317, saw Licinius acknowledge Constantine as his superior. The agreement required Licinius to cede European lands, excluding Thrace, and to execute Valens. The two emperors also appointed their sons as Caesars, establishing a fragile truce that endured for approximately seven years.
Source: Battle of Mardia
