Vikings were good architects too
 

Well, if they were building great trans-Atlantic seagoing ships by hand back in the 10th Century I suppose they could have built some pretty decent fortresses too.

They were some bad dudes. ;)

http://news.yahoo.com/ancient-viking...133135308.html

interestring, thanks for the link

Oh yeah they did. The Ulfbehrt sword is a powerful example. Great documentary on NOVA. You can watch it for free online. Brilliant shipbuilders, mariners and the worlds most effective amphibious assault force for hundreds of years. And here's the thing, they didn't just hitch a ride. They rowed. The Vikings were very fit and highly motivated for battle.

Viking architecture could be as sophisticated as their ships and often were built by the same people. Below are examples from 8th century onward to Eero Saarinen modern interpretation of same in the Hockey Rink at Yale University. In each structure you can see the link and the complex structures involved. The system provides a clear span uncommon to other systems of the time let alone strength.

Hockey Rink: https://www.google.com/search?q=hock...ed=0CAgQ_AUoAQ

These fortresses may have also been built by some of the slaves the Vikings brought back with them from their raids to the Westlands (England).

Many of those that the Vikings brought back with them from their conquests, adapted and integrated into the Norse communities, and brought with them a greater knowledge of buildings and fortresses.

This isn't saying that the Vikings didn't have the architectural experience or knowledge, but if it dealt with stone, that was more akin to that found in the British isles and mainland Europe.