A chance occurrence or event defines the start up of this place rather well.
No one wanted to move into this area and take over The Green. A swamp with many tales of horror told of it.
Rather by chance, a group moved into the area, and drew their border outside of The Green.
Nothing evil has invaded the Dukedom. No one has gone into the swamp to find out if its due to how the border was drawn.
Location map: