Prior to the First Punic War, Rome had a small fleet of about 20 triremes under the command of two officers known as the duoviri navales. It is estimated that at the height of the First Punic War Rome had a fleet of about 160 vessels and Carthage about 130, both sides being limited by the available rowers (as opposed to available material and builders).

During the war against Mithridates, Lucius Licinius Lucullus was sent to raise a fleet from the Mediterranean states allied with Rome. He travelled with four light sailing craft and three Rhodian galleys. Rhodes was firmly against Mithridates and this provided a core fleet from which he could add ships from other allies, such as Crete, Cos and Cnidus. It's unclear exactly how large this fleet was, but it had few if any Roman vessels. After the war, a permanent fleet of about 100 ships was formed from Rome's allies to protect the Aegean. This fleet might simply have been a continuation of Lucullus' fleet, in which case he would have had around 100 ships. Rhodes signed a treaty of alliance with Rome in 164 BC, and remained a firm ally for that time, although their privileges slowly declined due to Roman politics. While Rhodes was powerful, Rome relied on them for naval support in the Mediterranean.

In 43 BC Gaius Cassius Longinus attacked Rhodes, because it was allied to the triumvirs. At that point Rhodes had 33 galleys (probably biremes), and Cassius had 80 heavier ships (probably triremes, quinqueremes, or deceres). Cassius was successful in defeating and sacking Rhodes.

At Actium Octavian and Agrippa followed the example of the Rhodians in attacking heavier ships with lighter ones, and proved this could be a successful strategy. At Actium Octavian had a fleet of 250 warships, mostly liburnians with some hexeres. Antony and Cleopatra had 230 warships, mostly quinqueremes with some larger deceres, 30-50 transports and 60 Egyptian warships – of quinquereme size or larger, quite probably deceres. Octavian used groups of 3-4 liburnians against each larger warship.

Between Actium and the fall of the western empire the Roman navy consisted almost entirely of liburnians, which were cheap and fast, since Rome had no major opposition at sea.

Roman Decere (c.30 BC):
Length: 145 ft
Beam: (hull) 20 ft
(outrigger) 28 ft
Oar length (longest): 40 ft
Draught: 6-7 ft
Crew: 572 rowers, 15-30 sailors, 200-250 marines
Armament: 2 fighting towers, 2-6 catapults

Roman Liburnian (c.30 BC)
Length: 108 ft
Beam: 12 ft
Draught: 3-8 ft
Crew: 144 rowers, 10-15 sailors, 40 marines.