Keep an eye on the boss. To the untrained eye, building blocks from various periods resemble one another. But the raised central area (the boss), surrounded by a margin, is the tipoff to the date of the block. Shown here in head-on and side views is masonry from the Herodian period with a low, flat, smooth boss (top left); Herodian masonry with an unfinished boss, used below the intended ground level (top right); Hasmonean masonry with a rough, projecting boss (bottom left); and Persian masonry with a rounded, bulging boss (bottom right).