Arnold's army was prepared to confront the leader of the fire giants. While Arnold was not worried about being unable to handle Surtr on his own, he thought it would be good to at least be prepared for any uncertainties.
That was if they could find Surtr in the first place. Upon arriving at the place the other fire giant had pointed them towards, they arrived at the capital... or the place that had the ruins of such a place either way...
The city in front of them was the capital city of the fire giants. However, the city had already been obliterated, only ruins of the once-magnificent city had been left behind. At first, Arnold thought maybe the planet's crumbling had destroyed the place.
But the more he looked at the destroyed city, the more revelations popped up in his head. Although a fire giant's body disappeared after it was killed and became one with the planet, their weapons and armours did not.