Longships were a type of ship invented and used by the Norsemen (commonly known as the Vikings) for trade, commerce, exploration, and warfare during the Viking Age. The longship's design evolved over many centuries, beginning in the Stone Age with the invention of the umiak and continuing up until the 6th century with clinker-built ships like Nydam and Kvalsund. The longship appeared in its complete form between the 9th and 13th centuries. The character and appearance of these ships have been reflected in Scandinavian boat-building traditions until today. The particular skills and methods employed in making longships are still used worldwide, often with modern adaptations. They were all made out of wood, with cloth sails (woven wool) and had numerous details and carvings on the hull.
The longships were characterized as a graceful, long, narrow and light wooden boat, with a shallow-draft hull designed for speed. The ship's shallow draft allowed navigation in waters only one metre deep and permitted arbitrary beach landings, while its light weight enabled it to be carried over portages or used bottom-up for shelter in camps. Longships were also double-ended, the symmetrical bow and stern allowing the ship to reverse direction quickly without a turn around; this trait proved particularly useful at northern latitudes, where icebergs and sea ice posed hazards to navigation. Longships were fitted with oars along almost the entire length of the boat itself. Later versions had a rectangular sail on a single mast, which was used to replace or augment the effort of the rowers, particularly during long journeys. The average speed of Viking ships varied from ship to ship, but lay in the range of 5–10 knots (9.3–18.5 km/h) and the maximum speed of a longship under favourable conditions was around 15 knots (28 km/h).
The Viking longships were the epitome of naval power in their time and were highly valued possessions. They were often communally owned by coastal farmers and commissioned by kings in times of conflict, in order to quickly assemble a large and powerful naval force. While longships were used by the Norse in warfare, they were mostly used as troop transports, not warships. In the tenth century, longships would sometimes be tied together in offshore battles to form a steady platform for infantry warfare. During the 9th century peak of the Viking expansion, large fleets set out to attack the degrading Frankish empire by attacking up navigable rivers such as the Seine. Rouen was sacked in 841, the year after the death of Louis the Pious, a son of Charlemagne. Quentovic, near modern Etables, was attacked in 842 and 600 Danish ships attacked Hamburg in 845. In the same year, 129 ships returned to attack up the Seine. They were called "dragonships" by enemies such as the English because they had a dragon-shaped bow. The Norse had a strong sense of naval architecture, and during the early medieval period they were advanced for their time.