Trireme, ancient Greek warship with three files of oarsmen on each side, as well as sails, 38 meters/115 foot long. It was mentioned by Thucydides during the 8th century BC. It evolved from the early Phoenician and Greek armed merchant ships.

Remus is latin for oar and tri meaning the three tiers.

The earliest galleys were probably of single banks of oars, but the larger ones mentioned in the Iliad (with 120 rowers) were probably two-banked ships. The three-banked galleys first appeared about 700 BC.

The Athenian trireme was a galley of about 38 meters in length, a beam of 6 meters, a depth of 3 meter, and a draft of 1 meter. Although they had a square sail, the main method of propulsion was by three tiers of oars.

The lowest tier consisted of 27 oars per side and was called thalamites, the middle tier also had 27 oars per side and was called zeugites, and the oars on the top were called thranites. Unlike the other galleys all 170 oarsmen on the Greek trireme were freemen. They could row the galley at speeds of about 7 knots (13 km/h). The main weapon of the galley was the ram, an extension forward of the keel designed to penetrate enemy ships. A small number of soldiers were also carried.

As a war vessel the galley had many limitations. It was long and slender and therefore not particularly seaworthy. It had to be long so that enough oars could be put into each bank to give the vessel its essential speed. It operated best in calm water. In rough water the rowing beat of the oarsmen was thrown off and the ship rolled its lower oar parts under. Too great a length made them both weaker and easier to ram. The oars of a trireme were therefore arranged in three rows one above the other. That gave them greater strength and more speed for less length.

Romans constructed their trading vessels of pine or cedar, and reserved oak for their vessels of war. From the constructional viewpoint, there occur at this time the first examples of the various members of the hull which are in use today. The keel, ribs, planking and thwarts, which serve to brace the boat transversely as well as providing a seat for the oarsmen, came into being as a forerunner of what might be termed modern construction. Since vessels were usually beached during the winter months in the Mediterranean, the draft was necessarily limited and consequently the size of the craft remained quite small.

While Sparta had the most powerful army in Greece, Athens commanded the sea. Before the 5th century, sea battles had been fought much like land battles. The plan was to get close to the enemy, ram her, then board her and fight like soldiers. During the Persian wars, Athens developed new tactics in naval warfare.

The Athenians, who were natural seamen, not only had the biggest fleet, they also developed the most skilful tactics. Phormio, a commander in the Peloponnesian War, was able to pin the enemy into a circle at the battle of Naupactus by the better sailing powers of the Athenian ships. The enemy became more and more crowded, they began to bump into each other, and when they were in a real muddle, Phormio attacked.

Triremes had some drawbacks. Because they were shallow, they were in danger from the sudden storms which blow up in the Mediterranean. They had no space for sleeping or cooking, so they could never sail far from base. They could not, therefore, blockade a coast, as an army could blockade a city. As wars were often won by starving the enemy into surrender, that was a serious disadvantage.

The Persian Wars also featured a large sea battle with triremes forming part of the victorious Greek fleet at the battle of Salamis in 480 BC.

The great victory of the Greeks over the Persian fleet at Salamis was won by superior tactics. The Persian fleet was larger, and their ships were quicker and nimbler, but the Greeks lined up their ships across the entrance to a narrow strait, protected by the rocky coast on both sides. The Persians could not bring enough force against the concentrated Greek formation. They fell into disorder and suffered heavy losses.

It was the Greeks who learned most from this victory. They made their ships lighter and faster, and instead of simply driving straight at the enemy ships, they worked out movements by which they could disable them by breaking their oars.

Ancient Greek and Roman galleys were classified as biremes, triremes, quadriremes, and quinqueremes. These terms are commonly supposed to describe a galley as having from two to five vertical banks of oars.

The bireme was an earlier ship with only two tiers of oars, and the quadrireme and quinquireme, which are mentioned in connection with Dionysus of Syracuse. One interpretation is that they had two oarsmen on the upper tiers of oars. There is mention of ships with many more tiers of oars but these are considered unlikely. It is improbable that more than three vertical banks were ever used. The terms may possibly refer to groups of oars or perhaps to the number of men per oar.

The principal weapons of the early Greek military galleys were the ram, a sharp beak on the bow, and the catapult. Archers were used to release broadsides of arrows. Roman galleys, with an abundance of manpower in the form of slaves and prisoners to work the oars, carried soldiers to board enemy ships, were equipped with a corvus, a hinged drawbridge that could be lowered from the foremast. Spikes on the underside of the corvus drove into the enemy's deck and held the two ships together.

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