In the first season, Alfred asks Odda the Elder to raise the Somerset fyrd. In the final episode of the second season, Odda is an ealdorman of Devonshire and he raises the Devonshire fyrd.
The men are constantly sharpening their swords, and yet in closeups, the edges are completely flat, not even slightly sharp.
It is incorrectly said that Alfred's crown would not have borne the fleur-de-lis. Alfred The Great, on whom the character is heavily based, is depicted a plethora of times through history as wearing a crown bearing the fleur-de-lis.
A Dane in the 9th century would probably not have been named "Kjartan" as the name is a Norse appropriation of an Irish name that was adopted by the Norse-Gaelic settlers of Iceland.
The symbol for the House of Wessex is wrong. It is a well-documented fact that they used the Golden Dragon with a red background--especially on flags and banners.
The symbol for the Danes/Vikings is wrong. It is well-documented that they used raven images on their flags and other things. The reason is, the raven is Odin's messenger in Norse mythology.
Drinkers use wood or horn cups, but they clink together, sounding like glass.
Men often draw a sword from a leather sheath, but there is a metal-on-metal sound. However leather Sheaths usually have a metal collar around the opening, otherwise the blade would cut through the opening of the sheath when drawn.
It is incorrectly stated that the Danes would only use the raven symbol on flags and other objects. It is well-known that Norse warriors would use different symbols from tribe to tribe, much like a coat of arms or a family crest.
Lots of the women are seen wearing knitted shawls, often using a cable stitch. Knitting did not reach the British isles until the High Middle Ages, probably from the Middle East via Spain.
The Anglo-Saxons use kite-shields which where adopted in the 11th century, not the 9th.
The standard helmet of the Danes is based on the Ultuna helmet, which was used by a Swedish warrior almost 2 centuries prior to the events of the series.
Alfred's crown features the fleur-de-lis, which was not used by Anglo-Saxon royalty.
Most of the place names are spoken of using the contemporary names, but Winchester and Cumberland are more commonly referred to by their modern names.