Being seen on the battlefield was important long before the development of heraldry, and shields have always been an obvious vehicle for displaying that identity. The ancient Greeks bore shields with both collective and individual emblems, whilst the units of the Roman army carried a range of designs that, certainly from the late Roman period onward, distinguished them from each other.
Pre-heraldic display
For the early Middle Ages, we have little evidence for what, if any, system lay behind the decoration warriors bore on their shields. Occasional references
