In the Green Rider series, there is mention of a wall (D'Yer) surrounding the Blackveil forest. I've been trying to understand what the shape of this wall is. Is it a complete circle, have some kind of more interesting shape to it, or does it simply block off a large portion of land?
The D'Yer wall is based off of Hadrian's Wall http://www.american.edu/ted/images4/czhadwall.gif in the way that it crosses the country. The Dyer wall is much taller though and broader and has towers built into the length of it. It is magical as well as physical to hold back the spirit Mornhavon and the evil that has seeped into the Blackveil forest. There isn't any enemy other than Mornhavon on that side of the wall. He's just a spirit now so he couldn't sail around. Also It's been awhile since I've read the series but I believe the wall creates a magical field around the entire peninsula which means Mornhavon can't dig below the wall or even over it. Most of this is covered in the High Kings Tomb. I see there is a new book out though called the Blackveil I'll have to read it and see if there is something more.
I just read the book and IIRC, the forest is a peninsula and so the wall simply crosses it where peninsula meets the mainland, more or less.