The military costume of the Late Roman Period (late 3rd c. to mid 5th c.) was already quite distinct from the characteristic early imperial costume. The clothing had begun to resemble the Roman's Germanic neighbours with long-sleeve tunic and trousers, which began used among Legions stationed in Gaul and Germania and spread throughout the Empire.

While Infantry commonly wore Red tunics in combat, being the colour of Mars, God of War, the Marines instead wore Blue tunics to distinguish themselves. Blue being the colour of Neptune, God of the Sea. Despite its polytheistic origins, this practice would continue even after Christianisation in the mid 3rd century.