How a tactical maneuver at the Eurymedon River crippled Hannibal's final naval campaign
In August 190 BC, Hannibal faced the Rhodian fleet in a pivotal clash of the Roman–Seleucid War. Though he preserved most of his ships, the battle off Side left his fleet too damaged to reinforce the main Seleucid navy, effectively clearing the path for a Roman invasion of Asia Minor.
The Battle of the Eurymedon, or Battle of Side, emerged from the escalating tensions between the Roman Republic and the Seleucid King Antiochus III. After suffering a major defeat at Thermopylae in 191 BC, Antiochus sought to maintain his grip on Asia Minor. Hannibal, having fled to the Seleucid court in 196/195 BC, was tasked with building a new fleet in Cilicia to challenge Roman naval dominance. He focused on constructing large, multi-oared vessels, believing they would counter Roman boarding tactics, though wartime shortages significantly delayed his progress.
By July 190 BC, Hannibal set sail with a fleet of 47 warships, including seven heavy septiremes and hexaremes. The Rhodian admiral Eudamus, commanding a smaller but highly experienced force, intercepted the Seleucids at the mouth of the Eurymedon River in August. Despite initial confusion that briefly exposed a portion of the Rhodian line to Hannibal’s seaward wing, the Rhodians regained their composure. They employed the 'diekplous' maneuver—rowing through gaps in the enemy formation to strike the vulnerable sides and sterns of Seleucid ships.
The maneuver was devastating. Half of the Seleucid landward wing was heavily damaged, forcing a retreat. While Hannibal managed to withdraw his own squadron, the damage to his fleet was irreparable in the short term. This failure prevented him from linking up with the main Seleucid fleet at Ephesus under Polyxenidas. Isolated and lacking reinforcements, Polyxenidas was later defeated at the Battle of Myonessus, which solidified Roman control over the Aegean. This sequence of naval failures ultimately doomed Antiochus’s ambitions, as the Romans were then able to launch their decisive invasion of Seleucid Asia Minor.
Source: Battle of the Eurymedon (190 BC)
