The Ulfberht Long Sword was a straight-bladed, double-sided sword of medieval Europe, three feet double edged steel forged for hacking, slashing and stabbing. It was the Mid-Range weapon of the Viking.
The Long Sword had a straight blade with two cutting edges and a one-handed hilt with a lobed pommel. The blade had deep fullers running the length of the blade to lighten it. The weapon was about three feet long, although later swords were longer.
The Long Sword was capable of thrusting and slashing. Due to the relative shortness of the hilt, it was almost always used one-handed, wielded with either a shield, axe or another sword. The Long Sword (Celt) of the Germanic Celts were the primary inspiration of the Viking sword. These swords would later evolve into the Norman Broadsword and Medieval Broadsword.
Swords were somewhat uncommon with Vikings since they were so expensive; which is why the cheaper Great Axe was the more common melee weapon. However Viking nobles and officers could afford these swords.
In the show it was tested against the Naginata, and was given the edge. While the Samurai won by a thin margin on the whole, the Viking's sword was deadlier than any other weapon used by the Samurai or Viking.
The Viking Age and Early Islamic Golden Age occurred simultaneously. The Saif or Shamshir sword has similar characteristics to the Viking Long Sword.