Galea (helmet) in the context of "Galero"

The Roman legionary (in Latin legionarius; pl.: legionarii) was a citizen soldier of the Roman army. These soldiers would conquer and defend the territories of ancient Rome during the Republic and Principate eras, alongside auxiliary and cavalry detachments. At its height, Roman Legionnaires were viewed as the foremost fighting force in the Roman world, with commentators such as Vegetius praising their fighting effectiveness centuries after the classical Roman legionary disappeared.

Roman legionnaires were recruited from Roman citizens under age 45. They were first predominantly made up of recruits from Roman Italy, but more were recruited from the provinces as time went on. As legionnaires moved into newly conquered provinces, they helped Romanize the native population and helped integrate the disparate regions of the Roman Empire into one polity. They enlisted in a legion for 25 years of service, a change from the early practice of enlisting only for a campaign. Legionnaires were expected to fight, but they also built much of the infrastructure of the Roman Empire and served as a policing force in the provinces. They built large public works projects, such as walls, bridges, and roads. The legionary's last five years of service were on lighter duties. Once retired, a Roman legionary received a parcel of land or its equivalent in money and often became a politically prominent member of society.

The murmillo (also sometimes spelled "mirmillo", "myrmillo", or "mirmillones" pl. murmillones) was a type of gladiator during the Roman Imperial age. The murmillo-class gladiator developed in the early Imperial period to replace the earlier Gallus-type gladiator, named after the warriors of Gaul (Latin: Gallus, lit. 'a Gaul'). As the Gauls inhabiting Italy had become well integrated with the Romans by the time of the reign (27 BCE to 14 CE) of Augustus, it became undesirable to portray them as enemy outsiders; the Gallus-class gladiator thus fell out of use.

The designation murmillo originated with the Greek word μορμύρος (mormyrus) for a type of fish - murmillo gladiators could wear a Gallic-model helmet incorporating fish-imagery.