 "Stretchers" would be placed so the longer side was on the face of the wall, and "headers" would be placed so the shorter side was on the face of the wall, and would thus extend further back into the wall thickness.Various patterns could be produced by changing how the blocks were placed, and it was common to strengthen the wall by ensuring that the joints between blocks were centered over the blocks in the row below.With the introduction of Roman concrete, continuous outer walls were often constructed, with some blocks laid as headers in order to attach to the inner wall.