A trireme (from Latin triremis; literally 'three-oarer') was a type of galley; a Hellenistic-era warship that was used by the ancient maritime civilizations of the Mediterranean; especially the Phoenicians; ancient Greeks; Persians and Romans.

The trireme derives its name from its three rows of oars on each side; manned with one man per oar. The early trireme was a development of the penteconter; an ancient warship with a single row of 25 oars on each side; and of the bireme; a warship with two banks of oars; probably of Phoenician origin. As a ship it was fast and agile; and became the dominant warship in the Mediterranean from the 7th to the 4th centuries BC; when they were largely superseded by the larger quadriremes and quinqueremes. Triremes played a vital role in the Persian Wars; the creation of the Athenian maritime empire; and its downfall in the Peloponnesian War.