Stone walls are plentiful at Weir Farm. Some are substantial and seem taller than the ones I typically see in Groton, MA. Some are tumbledown, because as Robert Frost says, "Something there is that doesn't love a wall." The park service has a whole brochure devoted to the stone walls at Weir Farm, which fall into three categories: thrown walls, laid walls and rubble-filled walls. Thrown walls do not require any experience to build, and because of their lack of stability, required farmers to constantly rebuild them (the kind Frost was talking about in "Mending Wall"). Laid walls are built by masons with quarried stone. Rubble-filled, the most stable, are two laid walls constructed next to each other with the gap in between filled with rubble. Stone walls appear in J. Alden Weir's paintings, but I haven't attempted any (yet!).