Roman Culture/Roman Navy Ships
The war at sea in the classical era was all about well trained crews rowing their ships into enemy formations and either ramming them head on, or pulling in your own oars and sliding along the side of an enemy breaking all of its oars so they could no longer maneuver. Ships were equipped with a large bronze ram with three flat prongs under water at the bow. Oarsmen were below decks, and could propel the ship at up to fourteen knots, about seventeen miles per hour, the same speed as an average eighteenth century all sail warship. There was a partial deck on top for a few sailors and marines to stand on and the aft part of the ship where the commander and helmsman were was shaded with an awning. During the Hellenistic period ships got bigger, the successor kingdoms to Alexander were wealthy beyond the imagination of an early city state dweller. They built larger and larger ships in a naval race intended not for supremacy at sea, but for prestige. Larger ships were less maneuverable, but could hold more men and even large projectile weapons. This caused naval tactics to revert from speed, maneuverability, and ramming to disable an enemy to firing at them from a distance then boarding.
When the Senate decided on a course of massive naval expansion they had to decide what types of ships to build. There were six practical types available, and many variations on those different classes. The maximum numbers of ships a state could muster, man, maintain, afford, and coordinate in battle; in the ancient world was most likely three hundred. It is probable that Carthage had that many ships. Ships were classed based on how many oarsmen were stationed on a vertical bank of oars. Ships would have up to fifty oars per side in numerous horizontal rows. The prefix in the name refers to the number of oarsmen in a vertical set of oars followed by the suffix oar. 
The first and smallest type of ship available to the Romans was the hemiolia. This ship had a single row of oars. It was light and fast and its narrow draft and high speed made it well suited for commerce raiding, troop transportation, and littoral combat, especially in rivers. Slightly larger was the liburnian, a type of bireme with two banks of oars on each side ideal for scouting. It would become the mainstay of the Roman Imperial Navy, but had little use in large fleet engagements.  Next is the tried and true trireme, mainstay of the classical fleets of Greece. The most is know of this class, largely because one was reconstructed in the 1980’s. Their shallow draft and high length to beam ratio, combined with their three hundred rowers made these ships capable of great speed and maneuverability. They are lightly built and cannot carry many additional troops and like most ships of this period are not able to venture too far out from the coast. They are too narrow and shallow drafted to handle moderate waves. 
The quadrireme was smaller and slower than the trireme but it was more versatile. It had two banks of oars on each side and each oar had two men on it. This required a wider ship. The wider the ship the more stable she could be as a fighting platform and the more she could carry in terms of men and heavy weapons. With two men per oar the rowers did not have to be as experienced. They and the ships larger than them also could have had towers for archers to shoot down on enemies from. The mainstay of Roman and Carthaginian naval power was the quinquereme. These were heavy, slightly more seaworthy ships. The exact way their oars and oarsmen were arranged has yet to be determined but whatever the case these ships were wider than any of the others so far and could carry about one hundred marines. Hexaremes were the largest ships in the Western Mediterranean, usually reserved as fleet flagships. They are believed to have been wider, heavier versions of triremes with two men per oar instead of one. There were also larger ships called polyremes in the east with as many as forty rowers per vertical set of oars. These monsters were impractical to sail and were probably never used in battle. They were nothing more than a source of prestige for their owners. 
EDIT: 12-10-11 Rojen: scanned for spelling and plagiarism
 J. S. Morrison, J. F. Coates, and N. B. Rankov, The Athenian Trireme (Cambridge: Cambridge University Press, 2000), 258.
 Cecil Torr, Ancient Ships (Chicago: Argonaught Inc. Publishers, 1964) 9-13.
 Cecil Torr, Ancient Ships (Chicago: Argonaught Inc. Publishers, 1964) 54.
 J. S. Morrison, J. F. Coates, and N. B. Rankov, The Athenian Trireme (Cambridge: Cambridge University Press, 2000), 128.
 Cecil Torr Ancient Ships (Chicago: Argonaught Inc. Publishers, 1964) 55-57.