The Battle of London Bridge - S1.E9

In October 1013, King Sweyn leads a fleet of Danish and Viking ships in an attempt to take London Bridge of England. Askeladd's army, hired by the army of Denmark, was among them. However, after the betrayal of Thorkell the Tall, a Viking known for his overpowering strength, London Bridge has become impregnable. Askeladd tells Thorfinn he'll reward him with a duel if he's able to kill Thorkell.