Praefectus classis

The Roman navy (Latin: Classis, lit. "fleet") comprised the naval forces of the Ancient Roman state. The navy was instrumental in the Roman conquest of the Mediterranean basin, but it never enjoyed the prestige of the Roman legions. Throughout their history, the Romans remained a primarily land-based people and relied partially on their more nautically inclined subjects, such as the Greeks and the Egyptians, to build their ships. Because of that, the navy was never completely embraced by the Roman state, and deemed somewhat "un-Roman".

In Antiquity, navies and trading fleets did not have the logistical autonomy that modern ships and fleets possess. Unlike modern naval forces, the Roman navy even at its height never existed as an autonomous service but operated as an adjunct to the Roman army.

During the course of the First Punic War, the Roman navy was massively expanded and played a vital role in the Roman victory and the Roman Republic's eventual ascension to hegemony in the Mediterranean Sea. In the course of the first half of the 2nd century BC, Rome went on to destroy Carthage and subdue the Hellenistic kingdoms of the eastern Mediterranean, achieving complete mastery of the inland sea, which they called Mare Nostrum. The Roman fleets were again prominent in the 1st century BC in the wars against the pirates, and in the civil wars that brought down the Republic, whose campaigns ranged across the Mediterranean. In 31 BC, the great naval Battle of Actium ended the civil wars culminating in the final victory of Augustus and the establishment of the Roman Empire.

During the Imperial period, the Mediterranean became largely a peaceful "Roman lake". In the absence of a maritime enemy, the navy was reduced mostly to patrol, anti-piracy and transport duties. The navy also manned and maintained craft on major frontier rivers such as the Rhine and the Danube for supplying the army.

...
Wikipedia