section_path: Technology
section_name: Technology
paragraph_text: Technology
  
  The Vikings were among the most advanced of all societies of the time in their naval technology, and were noted in other technological works as well. The Vikings were equipped with the technologically superior longships; for purposes of conducting trade however, another type of ship, the knarr, wider and deeper in draft, were customarily used. The Vikings were competent sailors, adept in land warfare as well as at sea, and they often struck at accessible and poorly defended targets, usually with near impunity. The effectiveness of these tactics earned Vikings a formidable reputation as raiders and pirates.
  
  The Vikings used their longships to travel vast distances and attain certain tactical advantages in battle. They could perform highly efficient hit-and-run attacks, in which they quickly approached a target, then left as rapidly as possible before a counter-offensive could be launched. Because of the ships' negligible draft, the Vikings could sail in shallow waters, allowing them to invade far inland along rivers. The ships were agile, and light enough to be carried over land from one river system to another. "Under sail, the same boats could tackle open water and cross the unexplored wastes of the North Atlantic." The ships' speed was also prodigious for the time, estimated at a maximum of 14–15 knots (26–28 km/h). The use of the longships ended when technology changed, and ships began to be constructed using saws instead of axes, resulting in inferior vessels.
  
  While battles at sea were rare, they would occasionally occur when Viking ships attempted to board European merchant vessels in Scandinavian waters. When larger scale battles ensued, Viking crews would rope together all nearby ships and slowly proceed towards the enemy targets. While advancing, the warriors hurled spears, arrows, and other projectiles at the opponents. When the ships were sufficiently close, melee combat would ensue using axes, swords, and spears until the enemy ship could be easily boarded. The roping technique allowed Viking crews to remain strong in numbers and act as a unit, but this uniformity also created problems. A Viking ship in the line could not retreat or pursue hostiles without breaking the formation and cutting the ropes, which weakened the overall Viking fleet and was a burdensome task to perform in the heat of battle. In general, these tactics enabled Vikings to quickly destroy the meagre opposition posted during raids.
  
  Together with an increasing centralisation of government in the Scandinavian countries, the old system of leidang —a fleet mobilisation system, where every skipreide (ship community) had to maintain one ship and a crew—was discontinued as a purely military institution, as the duty to build and man a ship soon was converted into a tax. The Norwegian leidang was called under Haakon Haakonson for his 1263 expedition to Scotland during the Scottish–Norwegian War, and the last recorded calling of it was in 1603. However, already by the 11th and 12th centuries, perhaps in response to the longships, European fighting ships were built with raised platforms fore and aft, from which archers could shoot down into the relatively low longships. This led to the defeat of longship navies in most subsequent naval engagements—e.g., with the Hanseatic League.
  
  The Vikings were also said to have fine weapons. Generally, Vikings used axes as weapons due to the lessened amount of iron required for their creations; swords were typically seen as a mark of wealth. Spears were also a common weapon among Vikings. Great amounts of time and artistry were expended in the creation of Viking weapons; ornamentation is commonly seen among Viking weapons. Scandinavian architecture during the Viking Age most often involved wood, due to the abundance of the material. Longhouses, a form of home, often featuring ornamentation, are commonly seen as the defining building of the Viking Age.
  
  Exactly how the Vikings navigated the open seas with such success is unclear. While some evidence points to the use of calcite "sunstones" to find the sun's location, modern reproductions of Viking "sky-polarimetric" navigation have found these sun compasses to be highly inaccurate, and not usable in cloudy or foggy weather. The archaeological find known as the Visby lenses from the Swedish island of Gotland may be components of a telescope. It appears to date from long before the invention of the telescope in the 17th century. Recent evidence suggests that the Vikings also made use of an optical compass as a navigation aid, using the light-splitting and polarisation-filtering properties of Iceland spar to find the location of the sun when it was not directly visible.