Halfgate is the default version of Plainsgate. The only way to unlock Plainsgate is to take Azure as your final tour of duty during the Conquest and specifically order either the Chorus or both armies to defend Plainsgate.
An otherwise unremarkable pit stop that marked the eastern border of the great Stone Plains. It was helped by the fact that as far as Azure's cities went, it was one of the smallest and most impoverished settlements and was thus skipped over by the Chorus. Of course, that turned out to be quite the advantage in the long run, as it destined the village for... Not greatness, but notability. Due to the Stone Sea's great quakes, the village of Plainsgate was bisected, half of its buildings falling deep into the cavern below. From that point forward, it was known as Halfgate.