Once you’ve established your first capstone, and built up the body of the wall (Image 1) and fire brick, begin setting your capstones. In this project, experts are setting a front and back cap, so piece the capstone together so that it forms a continuous exterior and interior circle. The back cap will be placed over the fire brick, to hide it. Piecing the front and back caps together is very similar to working a puzzle, so consider dry setting your capstones all the way around before setting them in mortar. Dry-fit them so that the joint width is also consistent. The capstones should be level all the way around, so once the first cap is leveled and set, level all the other capstones off of that first stone with your four foot level (Image 2).