Drystone walls are walls made of stacked stone without the use of mortar. Four types of stones are used for drystone walls, cornerstones, base stones, mixed stones and cap stones. Cornerstones, base stones and cap stones should have at least two flat sides, bottom and top. A tie stone is a stone that is the same width as your wall. Tie stones are used to provide stability to the wall. Drystone walls are built in courses, with each course being one layer of stone. Walls two and a half feet high and lower are the easiest for homeowners to build.