Homework / test French to English Other Architecture

I'm trying to translate this term for a wikipedia article on a chapel called 'Chapelle Saint-Jean du Liget'. There is a section where it says 'n'en subsiste plus que le départ des murs gouttereaux au contact de la rotonde' which to me implies that there were walls surrounding the structure which is still standing in the present day. Which you can kind of tell from the following photo:
https://fr.wikipedia.org/wiki/Chapelle_Saint-Jean_du_Liget#/...
The problem is that there doesn't seem to be a reliable translation for this term, I have seen 'eaves wall' and 'lateral wall' but they don't seem to have the same quality to them. I have seen definitions of 'mur goutterau' that describe it as just a wall that supports a gutter but in this case it doesn't seem to have the same meaning.