Tireme (Lat. triremis; Gr. triêres), an ancient galley—especially a war-galley—having three banks of oars. Originally boats with one bank, then with other two banks of oars, were used. In the Persian and Peloponnesian wars triremes were the largest vessels employed; but at the time of Alexander we find that galleys with four and five banks had gradually come into favour. In the Punic wars the Carthaginians employed quinqueremes; and thenceforth the Romans constructed their war-vessels after the model of the Carthaginian quinquereme. At Actium Antony had nine and ten banked galleys. Under the empire the police of the seas was managed by smaller vessels, liburnæ; great war-ships were hardly required.
The banks of oars were elevated above each other, but not perpendicularly; the lowest rank of rowers having the shortest oars and easiest work. How the banks of rowers were arranged to allow all to have a fair share of the work has never been satisfactorily explained. The trireme or quinquereme was also provided with a square sail, which was used when the wind was favourable for voyaging to relieve the labour of the rowers, but was not employed in action. In the earlier times victory depended more upon the number and valour of the soldiers on board than upon the skill of the seamen. Latterly the aim of each trireme was not as before to grapple with its opponent, but to dash with the greatest momentum possible with its beak against the enemy's vessel, and strike it amidship, or, at any rate, disable his banks of oars on one side. Fighting men were not so much wanted for these tactics. The crew then of an Athenian trireme consisted of about 200 men, of whom 20 might be sailors, nearly the same number marines, and the rest rowers. A contrivance for strengthening the prow of the trireme and increasing its efficiency as a ram gave the Syracusans their final victory over the Athenians in the harbour of Syracuse. The Romans preferred to grapple and fight hand to hand. See GALLEY.