Classiarii (singular: Classiarius; from Latin classis "fleet") referred to all military personnel (from the highest rank of praefectus classis to the simplest rank of miles classiarius) and personnel assigned to the maneuvering of ships (e.g., velarii or remiges) or their construction/maintenance (e.g., fabri navales), as part of the Roman navy, an integral part of the Roman army.

Having asked the sailors for something (allowance) for their shoes, since they had to walk frequently from Ostia and Pozzuoli to Rome, Vespasian did not think it right not to have given them an answer, so he added that the order was to go barefoot, so much so that it is still done that way today [Suetonius' time].The core of a naval crew was formed by the oarsmen (in Latin remiges, sing.

Regarding high command, on the other hand, during the imperial period, with Augustus the praefectus classis became procurator Augusti, at the head of each permanent fleet.

These posts were initially filled by those who belonged to the equestrian order, or beginning with Claudius, by his freedmen, thus ensuring direct imperial control over the various fleets.

[18] Great expertise and responsibility was required of the classiarii, particularly of some key figures: Finally, it is estimated that there were about 40,000 to 50,000 classiarii during the Early Roman Empire, organized according to the following hierarchical structure: Other important roles on ships, probably falling within the group of immunes were, according to an inscription found at Kos during the First Mithridatic War: In order to prevent the boats from being recognized when exploring, they were dyed blue (the color of the sea waves), along with their ropes and sails, to better camouflage themselves.

[33] A Legio XVII Classica, i.e., naval, probably distinct from one under Octavian that bore the same numbering, was part of Mark Antony's army and had to disappear after his defeat at Actium.