Generally, when a ruler is represented barefoot, it is to indicate that he is of holy descent, i.e. a man sent directly from the gods with divine properties to lead the vast Roman Empire. His shield represents the battle and victory of the Parthians. By his feet is a personification of the god of love, Eros to show that Augustus is a descendant of Aphrodite Genetrix(parent). On the breastplate itself you have the personifications of the captive countries (Gaul and Spain) in the form of two human beings.