The town of Gie and it's environs are surrounded by a wall, this is indeed the single defining feature of the town.
The wall itself is grey stone, and at least sixty feet high. Itappears to be a 'natural' feature, rather than an artificial structure. At least, seen close up it looks more like a vertical rock face than anything made by human hands. Some areas, however, do apear to be manmade constructs, such as the gatehouse (fortifications?) Around the main gate.
The wall is hazardous to haibane; Just touching it can lead to the haibane in question becoming ill, and new feathers are warned against even aproaching it.