Architecture of Norway  The architecture of Norway has evolved in response to changing economic conditions, technological advances, demographic fluctuations and cultural shifts. While outside architectural influences are apparent in much of Norwegian architecture, they have often been adapted to meet Norwegian climatic conditions, including: harsh winters, high winds and, in coastal areas, salt spray. Norway's architectural trends are also seen to parallel political and societal changes in Norway over the centuries. Prior to the Viking Age, wooden structures developed into a sophisticated craft evident in the elegant and effective construction of the Viking longships. Following that, the ascent of Christianity introduced Romanesque architecture in cathedrals and churches, with characteristically slightly pointed arches, barrel vaults, cruciform piers supporting vaults, and groin vaults; in large part as a result of religious influence from England. During the Middle Ages, the geography dictated a dispersed economy and population. As a result, the traditional Norwegian farm culture remained strong, and Norway differed from most European countries in never adopting feudalism. This, combined with the ready availability of wood as a building material, ensured that relatively few examples of the Baroque, Renaissance, and Rococo architecture styles so often built by the ruling classes elsewhere in Europe, were constructed in Norway. Instead, these factors resulted in distinctive traditions in Norwegian vernacular architecture, which have been preserved in existing farms in the many Norwegian open-air museums that showcase buildings from the Middle Ages through to the 19th century; prominent examples include the Norsk Folkemuseum in Oslo and Maihaugen in Lillehammer, as well as extant buildings still in service on farms such as those in the Heidal valley. In the 20th century, Norwegian architecture has been characterized by its connection with Norwegian social policy on the one hand, and innovation on the other. Norwegian architects have been recognized for their work, both within Norway—where architecture has been considered an expression of social policy—and outside Norway, in several innovative projects. Construction in Norway has always been characterized by the need to shelter people, animals, and property from harsh weather, including predictably cold winters and frost, heavy precipitation in certain areas, wind and storms; and to make the most of scarce building resources. Until modern times, transportation infrastructure was also primitive, and builders largely had to rely on locally available materials. Thanks to new digging methods like topsoil excavation, archeologists have been able to further uncover the remains or foundations of 400 prehistoric houses that were previously hidden beneath the ground. Prior to this only 200 sites were immediately visible from the surface layer.