Just something I thought about based on details...
Presumably, there is some lore between the maps of "Ruins" and "Halls". We know the Vikings of Halls had planned an attack on the Ruins.
(Map of Ruins)
Unfortunately for those of the Ruins, they would soon fall to the strength of the Vikings...
When the Vikings first arrived at the Ruins, they attacked the smaller and weaker corners of Ruins. The Vikings successfully defeated the Towers as seen during Post-battle/alt Ruins and continued to the Strongholds...
(Viking Ships located on Post-battle)
(Corner Towers were destroyed during Post-battle)
The Strongholds were able to hold off the Vikings until they were surprise attacked! The quick, small ships of the Vikings were able to get around and behind the Strongholds, where they soon landed their fatal attack...
(Ladder placed to climb into the Stronghold)
(Vikings ships established on the cliffs behind Stronghold seen in aftermath/normal Ruins)
The Strongholds, now invaded, were unable to fight back and were destroyed...left in Ruins after the raid of the Vikings...