A border is used to identify the outer limit of the die design. The most common border is a circle of dots. Most often the border was created by drawing a circle around a center punch using a compass of some sort, making for a nice round circle. Many older coins have a square board on the reverse; often the entire design is in an incuse square created by using a square punch as a reverse die. Other border types include linear (a solid line), fillet or bead and reel (appears as a dot-dash-dot-dash pattern), and double linear (found on later Byzantine coins). A crenelated border has repeated square indentations and projections symbolic of battlements and intended to represent a strong defensive city wall or fortification.