Galley, a narrow, single- or half-decked ship propelled by oars and sails. Most galleys had only one sail and depended chiefly on the rowers for motion. The galley originated on the Mediterranean Sea during ancient times. Most galleys were built as warships and were equipped with a ram at or below water level.

Warships of the ancient Greeks were biremes, galleys with two tiers of oars, and triremes, galleys with three tiers of oars. Greek naval tactics were to sink the enemy vessel by ramming it or to board it and fight hand-to-hand.

The Roman galleys, most of which were probably triremes, carried large numbers of well-trained soldiers, and the Romans devised new and more effective boarding techniques. The Byzantine bireme dominated the Mediterranean Sea during the early medieval period. Its chief weapon was Greek fire, flaming substances shot through a tube or hurled in fire-pots by catapult.

During ancient times, rowers for war galleys were either citizen conscripts or paid foreigners. Merchant galleys, however, often used slaves both as deck hands and as rowers. Beginning in the 15th century, navies began using convicts and prisoners of war as rowers.

The Viking longships, which raided northern Europe during the 9th and 10th centuries, were similar to galleys, but narrower and lighter. The rough waters of the northern seas were unsuitable for true galleys.

Genoa and Venice became leading Mediterranean powers in the 1300's and 1400's with their large trading galleys and war galleys with cannons mounted on the bow. The last important engagement fought between galleys was the Battle of Lepanto (1571), when the allied forces of Spain and Venice defeated the Ottoman Turks. By the 16th century galleys had become outmoded, because sailing ships were more maneuverable and could carry more guns. There was a dogmatic conviction among many naval experts of the day, however, that oared vessels were needed in sea fights in the Mediterranean, and galleys continued to be built until the early 18th century.