Today I did a study of a "sunken ruin" in a nearby forest. It was getting dark, sorry for the photo quality.
I think it collapsed because the river undermined parts of the structure. And then it broke at it's weakest spot (where I think there was some sort of metal plate, acting as a watergate).
Have a Happy St. Patrick's Day, Streak Club! My webcomic characters Petra and Battista!
(little known fact: I'm part Irish from my Mom's side. ;) )