The Battle for Kattegat is a military engagement for the ability to rule Kattegat. It depicts the confrontation between Ragnar and Lagertha's forces against the forces of Jarl Borg. The event takes place in Season 2 Episode 5, Answers in Blood.
Prelude
Jarl Borg has taken control of Kattegat in revenge for Ragnar and King Horik leaving him out of the Wessex raid. Word has reached Ragnar in Wessex that his family has fled, and his rule has been usurped. Ragnar and his warriors immediately sail home. They arrive at Floki and Helga's home where Helga tells Ragnar that Siggy had sent a messenger telling her where they were hiding. She will take them there the next day.
The next day, Ragnar is reunited with Rollo, Siggy, Aslaug, and his sons Ubbe, Hvitserk, and his newborn son Sigurd. Despondent at their small number of warriors, they are surprised by the arrival of Lagertha, Bjorn, and a contingent of warriors from Hedeby.
Since Ragnar and Lagertha's armies are unable to match Borg's in size, and because Borg is too safely entrenched in Kattegat, Rollo comes up with a plan to drive Borg out into the open. They will destroy the winter food supplies. Ragnar volunteers himself and Bjorn to complete the mission. Once a distraction is made, Ragnar and Bjorn make their way to the food storage where they kill the men guarding it. They successfully burn down the structures, leaving a blazing fire.
The ploy successfully draws Borg and his men out in pursuit of revenge. While out searching for Ragnar, Borg and his men come across a dead man, which is only a trap that leads them straight to Ragnar and his warriors, including Lagertha and her shield-maidens, waiting for them. At that same moment, Aslaug has a vision of the fight.
The Battle
Lagertha leads the charge. Bjorn proves himself as a warrior. Ragnar slices down almost thirty warriors in quick succession. Ragnar and Rollo finally act like true brothers and team up against their common enemy. The battle is short and bloody. Rollo kills a significant amount of Borg’s men with nothing but a shield and an axe. The death toll rises when Borg orders his men to ambush the Vikings, knocking them off their feet, including Bjorn. Ragnar runs to his son’s side and protects him. Bjorn kills several men during the fighting. Throughout the battle Ragnar and Borg eye each other across the field. Neither quite able to get to the other.
Aftermath
The battle is a victory for Ragnar and his forces. Jarl Borg and his forces are driven out of Kattegat and forced to return to Götaland. Ragnar is once again the Earl of Kattegat. Rollo congratulates Bjorn on fighting well, but Ragnar says he still has much to learn and is clearly disappointed in him.
As the triumphant group walks back into Kattegat, they are greeted by grateful residents. Many are excited and surprised to see Lagertha after so long. Aslaug can't help but notice how much more popular Lagertha is than herself or Siggy. The town gathers to offer a sacrifice to Odin in the form of a captured warrior of Borg's. As Rollo goes to behead the man, Ragnar interrupts and has Bjorn complete the sacrifice.
