Primarily used for warfare, these long and impressive looking ships were also used for trade. Until the late 16th century, when the bigger and much better armed galleon replaced it, the galley was the main warship of European naval forces.
The oldest galleys were Greek and Phoenician vessels of classical times. There were several types, classified by size.
The biggest (invented by the Phoenicians about 700 BC) were the so called biremes. They were not new; actually it was a transformed Egyptian model. The galley's underwater hull (hull - the body of the vessel) was much narrower than the other types of ships. The length to beam was surprisingly big, which made it really steady during rough sea. Usually if a boat has big length to beam, it is very firm, especially against heeling; it is almost impossible to topple them over. The boat looked very aesthetically with its rounded yet long and lean body.
Later, Greeks designed their own galley with a single mast. Its sail marked a revolution in thinking of men and effectiveness of the whole vessel - the big rectangular sail could be furled (to furl - to roll a sail up snugly on a yard or boom, and secure it). Furling enhances significantly the speed, influences directly the maneuvering of the vessel. Controlling it is like controlling the gear box of a car - its force. When going to war, the Greeks took a bronze-covered ram in their galleys - it was used to crash enemy vessels.