A vast network of roads and trade routes.
Hope that answered your question! :)
A, all the other answers would not make sense in the question.
The right term that is used usually to describe a region just beyond or at the edge of a settled area is a <u>Frontier</u>, because in that context, a frontier is a place or imaginary line that limits a region, territory, location, city or a country extension, and where sometimes the frontiers are located further or at the border of a settled area.
