The naval battle off Tauris Island in the Adriatic Sea was fought between Caesarean and Pompeiian forces after the Great Roman Civil War. The opposing fleets clashed at such close quarters that melee combat essentially decided the battle.
After the Great Roman Civil War and the Battle of Pharsalus, while Caesar was claiming his just desserts in Alexandria and Egypt, some remnants of the losing faction, Pompey’s Optimates, persisted in rebellion. They were mostly natives of Illyria (modern: Croatia, Montenegro, Bosnia and Herzegovina, and Albania) and were led by Marcus Octavius, one of Pompey’s old admirals. They were resisting the military and governmental presence of Caesar’s soldiers and Caesar’s quaestor and pro-praetor, or acting governor in the region, Lucius Cornificius. So, as best he could, Cornificius governed lightly trying not to draw the ire of the unruly locals. However, a series of violent conflicts initiated by the Pompeiians, aroused by the movements of Caesar’s troops, culminated in a naval battle.
In March of 47 B.C. Marcus Octavius began blockading ports in the region. One Publius Vatinius was called in by Lucius Cornificius to assist against the Pompeiians. Octavius possessed a potent naval fleet and was waging war along the Dalmatian coast. Vatinius, on the other hand, had only a few warships and some many small, fast boats. These he equipped with beaks, or metal-wooden protrusions affixed to the bow or front of the ships, and used them to ram into the enemy. He outfitted these ships with veteran legionnaires who had been recovering on sick leave in Brundisium (modern: Brindisi, Italy). And, so, set out towards Epidaurum (modern: Cavtat, Croatia) where Marcus Octavius was blockading another harbor.
Both parties, unbeknownst to each other, then sailed north toward the island of Tauris (modern: unknown, likely Sipan Island, Croatia, or some island near or north of Dubrovnik, Croatia). Once near the island, unaware that Octavius was there too, Vatinius’s fleet was caught off guard by the approach of an enemy ship. They had been totally out of formation, spread wide and apart from each other to avoid crashing due to a storm presently at sea there.
Well, when battle lines were drawn, it was clear and apparent that Vatinius was outmatched and outnumbered, for Octavius possessed more ships, and them being warships, more power. Vatinius’s one upperhand was his flagship, a quinquereme (a ship with five oarsmen per row, compared to a trireme for example with its three oarsmen). Octavius’s flagship was a quadrireme (four oarsmen per row), a mighty ship yet still lesser to the grandest of the time, the quinquereme.
Vatinius with full confidence in his veteran men and their presently high morale, lowered his sails and raised his flag to signal the attack and rowed head on into Octavius’s advancing quadrireme with such aggression – both achieving a high velocity – that the beak of Vatinius’s quinquereme pulverized and knocked away Octavius’s beak and further lodged itself into the quadrireme’s hull so that the two became interlocked and that all around these two now a naval battle raged.
The officers on each side came to their captain’s flagship’s side and so arose a naval combat in such close quarters that the size and numbers of the two opposing fleets mattered less and was rendered equal. The battle shifted from ship-to-ship combat to hand-to-hand combat as the two sides began boarding each other’s ships.
The freshness and bravery of Vatinius’s newly restored veteran legionnaires from Brundisium proved to be the key, deciding factor. As the ships all became interlocked, they were able to board each other’s decks and beat up the rebels. Bodies who had not been tossed overboard leapt over to escape, and where a man was not killed, there was a flight. So sudden, large, and panicked was this rout of Marcus Octavius’s fleet that the pinnaces, or rowboats, capsized by the weight of so many men attempting to climb aboard them. Even Marcus Octavius’s pinnace capsized, but he was able to swim to one of his light galleys and escape into the night towards Greece, then roundabout to Sicily with aim for Africa. From his fleet was won one quinquereme, two triremes, eight galleys, and many rowers and sailors by Vatinius.
As such, Vatinius achieved a glorious victory for himself, and ergo for Caesar as well. This win secured the province of Illyria (modern: Croatia, West Balkan Peninsula), stamped out the last remnants of the Pompeiian faction, and ended all traces of the Civil War there.
Source: Caesar. Civil War. Edited and translated by Cynthia Damon. Loeb Classical Library 39. Cambridge, MA: Harvard University Press, 2016.