How accurate is the show Vikings?

I saw someone posted about GoT so I will ask about another show I absolutely love. I want to know specifically about the battles. In the show you see the Vikings easily conquer and defeat countless English armies. All these armies have long swords, shields, armor, etc. and the Vikings just walk into their arrows and spears, and just bull rush through them and break through English lines. I know the English shield walls were supposedly weak by the time of the Viking invasions but that still sounds far fetched. All these battles are done in a very similar fashion with some minor changes each time. <br><br>Also, was Ragnar really the one who raided England? I know the name Ragnar was absolutely used by a real Viking leader, but it is said to have been different guys in different stories so I wonder if Ragnar was like King Arthur, a made up character to tell stories around. <br><br>If you have any sources you can share I’d appreciate them.