Pileus pannonicus

The Pannonian cap (pileus pannonicus) is a round-shaped cap used by the Roman army as early as the 3rd century AD, though it originates from Persia or the western part of the Balkan peninsula.
It was widely used for its simple shape and was sewn using wool, felt, leather or coarse fabrics. It was also used by Roman soldiers as padding to support the weight of their helmet during military battles, as reported by Vegetius at the end of the 4th century AD in Epitoma rei militaris I, 20.
Among the various iconographies that have been passed down to us, the pileus pannonicus is documented in the decorative elements of monumental works such as the Arch of Constantine and was also worn by high-ranking figures, as shown by the Portrait of the Four Tetrarchs statue group in Venice.