During the Hellenistic period, the light trireme was supplanted by larger warships in dominant navies, especially the pentere/quinquereme. The maximum practical number of oar banks a ship could have was three. So the number in the type name did not refer to the banks of oars any more (as for biremes and triremes), but to the number of rowers per vertical section, with several men on each oar. The reason for this development was the increasing use of armour on the bows of warships against ramming attacks, which again required heavier ships for a successful attack. This increased the number of rowers per ship, and also made it possible to use less well-trained personnel for moving these new ships. This change was accompanied by an increased reliance on tactics like boarding, missile skirmishes and using warships as platforms for artillery.
Triremes continued to be the mainstay of all smaller navies. While the Hellenistic kingdoms did develop the quinquereme and even larger ships, most navies of the Greek homeland and the smaller colonies could only afford triremes. They were used by the Diadochi Empires and sea powers like Syracuse, Carthage and later Rome. The difference to the classical 5th century Athenian ships was that they were armoured against ramming and carried significantly more marines. Lightened versions of the trireme and smaller vessels were often used as auxiliaries, and still performed quite effectively against the heavier ships, thanks to their greater manoeuvrability.
With the rise of Rome the biggest fleet of quinqueremes temporarily ruled the Mediterranean, but during the civil wars after Caesar’s death the fleet was on the wrong side and a new warfare with light liburnas was developed. By Imperial times, Rome controlled the entirety of the Mediterranean and thus the need to maintain a powerful navy was minimal, as the only enemy they would be facing is pirates. As a result, the fleet was relatively small and had mostly political influence, controlling the grain supply and fighting pirates, who usually employed light biremes and liburnians. But instead of the successful liburnians of the Greek Civil War, it was again centred around light triremes, but still with many marines. Out of this type of ship, the dromon developed.
Source: Wikipedia
